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ECON20110 Fall 2013 - Lecture 9: Monopoly — Transcript

by Glen Weyl · 9,518 words · 1,436 segments · language en · Watch on YouTube

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  1. 0:01okay so um the basic
  2. 0:06idea uh of the monopo model is that
  3. 0:09firms want to try to reduce their
  4. 0:12quantity in order to raise the price
  5. 0:14that they receive for their goods in the
  6. 0:16industry and the reason is that um in
  7. 0:19order to sell more units a firm needs to
  8. 0:23lower its price but not just on that
  9. 0:25last unit but on all of the units that
  10. 0:28the firm sells
  11. 0:30and this of course wouldn't arise if
  12. 0:32firms could charge different prices to
  13. 0:34each purchase and each purchaser which
  14. 0:36is something we'll talk about uh just
  15. 0:39after the
  16. 0:40midterm um okay so the Monopoly um will
  17. 0:46tend to reduce quantity below the point
  18. 0:48where price is equal to marginal
  19. 0:50cost and that basic effect is something
  20. 0:54that shows up all over uh the world so
  21. 0:58um Adam could you give me some examples
  22. 1:00of cases where firms with Market power
  23. 1:02reduce their quantities below what you
  24. 1:04would might think is an efficient
  25. 1:08level maybe something like uh you VI
  26. 1:11like a like a organization like a union
  27. 1:14or something is like a kind of like a
  28. 1:16monopoly of the labor yeah so like they
  29. 1:19might have like um they may try to like
  30. 1:23compat others entering into the the
  31. 1:26Labor Field or have some like license
  32. 1:28for the that's a very good example
  33. 1:31occupational lure uh we didn't talk
  34. 1:33about that in the first class we did in
  35. 1:35the previous years uh labor unions who
  36. 1:38try to stop immigration or have closed
  37. 1:40shops that stop people from competing um
  38. 1:43Farm cooperatives try to prevent
  39. 1:45overproduction of farm products uh drug
  40. 1:48cartel's main job is not to produce
  41. 1:51drugs but to stop other people from
  42. 1:52producing drugs uh and this is the
  43. 1:55reason that when the drug bar in Pablo
  44. 1:57Escobar was killed the price of cocaine
  45. 1:59fell precipitously rather than Rising um
  46. 2:04uh drug companies make massive
  47. 2:06investments in trying to reduce the
  48. 2:10supply of the goods that um they sell by
  49. 2:15stopping re-importation from poor
  50. 2:17countries of their products uh strictly
  51. 2:19delineated territories Etc digital
  52. 2:22materials of All Sorts are basically
  53. 2:25free to copy but not free to copy
  54. 2:28because the law tries to stop you from
  55. 2:30doing that and companies invest a huge
  56. 2:31amount in trying to reduce the quantity
  57. 2:34uh that's supplied movie theaters it
  58. 2:36basically cost nothing if a movie isn't
  59. 2:39sold out for an additional person to
  60. 2:41come and yet they keep people out by
  61. 2:43charging a price uh which is also
  62. 2:46obviously
  63. 2:46inefficient okay so to
  64. 2:49represent uh this let's say that the
  65. 2:53revenue that a monopolist earns R of Q
  66. 2:56is equal to their price which depends on
  67. 2:58quantity times quantity now under
  68. 3:00perfect competition they would set price
  69. 3:01equal to marginal cost and now they're
  70. 3:03going to set marginal revenue equal to
  71. 3:05marginal cost marginal revenue is just
  72. 3:06the derivative of the revenue and uh
  73. 3:10where's
  74. 3:11Joan ah there she is hi by the product
  75. 3:14rule what is the derivative of Revenue
  76. 3:17what's the marginal revenue equal to
  77. 3:21um plus der
  78. 3:26PQ so
  79. 3:28PQ p Q um so what's the derivative of P
  80. 3:33of Q * Q yeah P Q Plus p q with Q time Q
  81. 3:41yeah so oh yeah P of Q yes P of Q um
  82. 3:46plus P Prime * Q that's right
  83. 3:49absolutely um so there are two terms
  84. 3:53here but you're going to set this equal
  85. 3:54to marginal cost now if this first term
  86. 3:56was the only thing here then you would
  87. 3:57set price equal to marginal cost that
  88. 3:58would be good right this is what happens
  89. 4:02this is the term that comes from how
  90. 4:03much benefit the firm gets from changing
  91. 4:05its quantity holding the price fixed
  92. 4:06taking itself as a price taker but
  93. 4:09there's a second term that comes from
  94. 4:10the impact it has on price experienced
  95. 4:13on all of its infam marginal units
  96. 4:15that's the second term which is called
  97. 4:17Market power or the Coro Distortion or
  98. 4:19sometimes um the marginal surplus of
  99. 4:23consumers because what this term is is
  100. 4:26how much when the quantity increases
  101. 4:28consumers benefit
  102. 4:30which uh The Firm doesn't get right so
  103. 4:33the price is the marginal value that um
  104. 4:38consumers place on getting the product
  105. 4:40but not all of that goes into Revenue
  106. 4:42some of that goes into consumer surplus
  107. 4:44and that's exactly what this term is
  108. 4:48here
  109. 4:50okay
  110. 4:52um so this term is proportional to how
  111. 4:55many infam marginal units The Firm has
  112. 4:57and how much impacts price and those are
  113. 5:00both measures of how large the firm is
  114. 5:01if the firm is very small it will have
  115. 5:03little impact on price and will have few
  116. 5:05units on which to uh have that impact
  117. 5:09okay so let's derive some simple
  118. 5:12examples of this for the most common
  119. 5:14demand curves let's first start with a
  120. 5:16concave demand
  121. 5:17curve
  122. 5:19um and uh philli could you derive the
  123. 5:23marginal revenue curve corresponding to
  124. 5:25this demand curve uh should I go up to
  125. 5:28the board sure that's probably easiest
  126. 5:30for people to follow all
  127. 5:40right
  128. 5:43oh
  129. 5:45okay I can yeah
  130. 5:49please okay so Mr the piece of Q
  131. 5:54equals P of Q equals um
  132. 6:001 -
  133. 6:02q^2 right yeah and
  134. 6:06then uh Revenue
  135. 6:09= QP
  136. 6:12= uh Q 1 - Q 2 = Q - QB exactly and so m
  137. 6:22r is just a derivative which is Q - 3 q^
  138. 6:252 1 - 3 q^2 right yeah exactly well done
  139. 6:31philli thank you
  140. 6:35um
  141. 6:36okay so um let me show you what that
  142. 6:42looks like so here's the concave demand
  143. 6:46function and you see that as the
  144. 6:48quantity increases initially marginal
  145. 6:51revenue and uh and price are at the same
  146. 6:57point but then they diverge increas inly
  147. 7:00rapidly as the quantity
  148. 7:02increases
  149. 7:04okay um Andrew Adair is not
  150. 7:09here
  151. 7:12um Can someone else derive this for
  152. 7:15linear
  153. 7:16demand uh so yeah sure so first you find
  154. 7:20Revenue which is 1 - Q * Q so that's Q -
  155. 7:24q^2 take the Der of that you get 1 - 2 Q
  156. 7:28exactly so so this is steeper than
  157. 7:31demand is so here's linear demand this
  158. 7:34is steeper than demand is but it
  159. 7:36diverges at a constant rate right
  160. 7:39whereas this diverges from demand at an
  161. 7:41increasing
  162. 7:43rate okay how about um exponential
  163. 7:47demand uh Rishi can you derive sure uh
  164. 7:51yeah sure
  165. 8:09I'm just going right up
  166. 8:10here C
  167. 8:13is uh
  168. 8:20pus
  169. 8:25yeah so you got uh
  170. 8:37Q mhm can I erase this part is
  171. 8:43yeah I don't think we have an eraser
  172. 8:45again oh there there it
  173. 8:51is right so if you derive this you get
  174. 8:551us the bar of this so you get 2 * 1 2
  175. 9:03yeah plus
  176. 9:07uh no he's got a minus around the whole
  177. 9:09time
  178. 9:11yeah * 1
  179. 9:15yeah so you get 1 - 1 + log Q which is =
  180. 9:22to log Q
  181. 9:26exactly uh actually negative log q but
  182. 9:29oh
  183. 9:30yeah but no that's
  184. 9:32right okay so this one notice that
  185. 9:36that's like log q and it was 1 minus log
  186. 9:39Q so this is just by a constant below uh
  187. 9:44price right so that is shown in this
  188. 9:48graph here you see there's always a
  189. 9:49constant distance between marginal
  190. 9:51revenue and price so here they were
  191. 9:53diverging at an increasing rate here
  192. 9:55they're diverging at a constant rate
  193. 9:57here there's a constant distance between
  194. 9:59them so guess what's going to be
  195. 10:01happening with the last case that I give
  196. 10:03you uh reishi I'm going to call on you
  197. 10:06again uh do it for the constant
  198. 10:08elasticity all
  199. 10:12right
  200. 10:21not cool so I'm just going toise one
  201. 10:33so we have one
  202. 10:35over 12 right
  203. 10:39yeah which
  204. 10:42is yeah so
  205. 10:47sorry so you take
  206. 10:51q q * Q you get Q * Q * 1
  207. 11:0112 yeah and uh if you derive this you
  208. 11:04get
  209. 11:0712 12 Q to the 12 which is equal to 1
  210. 11:13over 2K
  211. 11:15Q exactly so notice that this is
  212. 11:21half of the price
  213. 11:26right and it's decreasing in p uh
  214. 11:30quantity so that means that these things
  215. 11:32are going to converge together over time
  216. 11:34right because there's a constant ratio
  217. 11:36between them rather than there being a
  218. 11:38constant difference between
  219. 11:41them so that's shown here you see
  220. 11:44they're further apart up here because
  221. 11:46the ratio between the two of them is
  222. 11:48always
  223. 11:49constant okay now how do we find Optimal
  224. 11:53quantities well imagine that the
  225. 11:55marginal cost were the x-axis here just
  226. 11:58for fun
  227. 11:59then you intersect that with the
  228. 12:01marginal revenue curve you draw a line
  229. 12:03up to the demand curve and left over to
  230. 12:05price in order to get uh the optimal
  231. 12:08price for the firm to
  232. 12:09charge okay now another way to write
  233. 12:13marginal revenue is as price time
  234. 12:16quantity sorry price of quantity uh Time
  235. 12:191 minus 1 over the elasticity of
  236. 12:22demand and uh reishi I'm going to have
  237. 12:25you dve that again as well
  238. 12:34I swear it's
  239. 12:44[Music]
  240. 12:54random 1 - one Epsilon is that yeah okay
  241. 13:04um so no it's not P of Q equals that
  242. 13:06it's marginal I want to claim that
  243. 13:08marginal revenue is equal to P of Q * 1
  244. 13:12- 1 Epsilon the question is how could
  245. 13:14you prove that that's the
  246. 13:20case um times P of Q
  247. 13:26oh so we have a we had a form for
  248. 13:29marginal revenue before can you
  249. 13:30transform it into that um okay so we had
  250. 13:35from before that marginal revenue
  251. 13:39equals P Q Plus it's p Prime of Q * Q
  252. 13:46sorry I pime of Q * Q Plus p q yeah
  253. 13:52okay
  254. 13:56um so
  255. 13:59if
  256. 14:03you well here you've got your P of Q
  257. 14:06term right which shows up there so this
  258. 14:08much must correspond to this term
  259. 14:10somehow right okay so I mean if you got
  260. 14:14your cuz you don't have a p of Q um
  261. 14:18unless
  262. 14:20you so why don't you try factoring a p
  263. 14:23of Q out of the whole expression P of Q
  264. 14:26yeah okay
  265. 14:29then you get 1
  266. 14:33plus
  267. 14:37um yeah
  268. 14:391 p
  269. 14:44q q q over
  270. 14:47PQ okay now oh okay does that look like
  271. 14:51an elasticity yes it is so right which
  272. 14:56you which is equal to yeah yeah two
  273. 15:01* 1
  274. 15:05plus right except that the elasticity of
  275. 15:08demand is negative so yeah exactly just
  276. 15:12to be a little bit more explicit this is
  277. 15:14DP DQ which is 1 over uh DQ
  278. 15:19DP right and then it's divided by you
  279. 15:22know q and multiplied by P and that's
  280. 15:25exactly the elasticity
  281. 15:27formula what did you say
  282. 15:29no you're done you're done my
  283. 15:33friend um okay so one thing that
  284. 15:36immediately tells us is that marginal
  285. 15:37revenue is negative whenever the
  286. 15:39elasticity of demand is less than one
  287. 15:42which means that the monopolist will
  288. 15:44never produce in a region where demand
  289. 15:46is in elastic because he'd always have
  290. 15:48an incentive to reduce his
  291. 15:50quantity um which would also reduces
  292. 15:53cost so the elasticity of demand can be
  293. 15:57seen as one thing one way of formalizing
  294. 16:00the notion of Monopoly power if the
  295. 16:02elasticity is small then the relative
  296. 16:05importance of that firm is small um if
  297. 16:09the elasticity is large that firm is
  298. 16:12relatively important to the market and
  299. 16:14it summarizes the notion of being sort
  300. 16:16of a big player and rearranging this
  301. 16:18setting uh this equal to marginal cost
  302. 16:21yield that the price minus marginal cost
  303. 16:24divided by Price that's called the
  304. 16:25relative markup is equal to the inverse
  305. 16:27elasticity of demand so the smaller the
  306. 16:30elasticity is the larger the markup The
  307. 16:32Firm charge is which is a natural
  308. 16:33measure of Monopoly
  309. 16:36power okay now of course there's other
  310. 16:39measures of Market power you could also
  311. 16:41create it's not obvious this is the best
  312. 16:43one another one you could create is the
  313. 16:45markup divided by the marginal cost
  314. 16:47rather than divided by the price and
  315. 16:49that's equal to 1 over the elasticity
  316. 16:51minus one or you could do the price to
  317. 16:53marginal cost ratio which is equal to
  318. 16:54the elasticity over the elasticity minus
  319. 16:56one or you could do the absolute markup
  320. 16:59which is equal to the price divided by
  321. 17:00the elasticity these are all very
  322. 17:02similar ways of measuring Market power
  323. 17:05um and some are more useful than others
  324. 17:07depending on the context so the standard
  325. 17:10learner formula is useful because it's
  326. 17:12so simple and it uses elasticity so
  327. 17:15directly the price cost ratio is
  328. 17:18useful uh for profits um especially when
  329. 17:23you have a constant marginal cost um
  330. 17:26because it yields just like the ratio
  331. 17:30between whatever the cost is and however
  332. 17:32much uh profits the firm is making um
  333. 17:37the uh markup to cost gives a measure of
  334. 17:41profitability the absolute markup is
  335. 17:44useful when costs are not positive which
  336. 17:46can happen for example in credit cards
  337. 17:49you know your credit card subsidizes you
  338. 17:52for using your card you get points for
  339. 17:54using your card because they're earning
  340. 17:56money off of interchange fees from
  341. 18:00Merchants that pay them when they use
  342. 18:01the card and so denominating things by
  343. 18:04cost can be problematic then
  344. 18:08um okay now of course to set these
  345. 18:12prices firms need to know what the
  346. 18:13demand curve is otherwise the quantity
  347. 18:16that they produce will not match uh
  348. 18:18demand and um to so as a result firms
  349. 18:23need to be able to draw out their
  350. 18:25marginal revenue curve and it used to be
  351. 18:28that firms just had to guess about this
  352. 18:30and gradually learn but the internet has
  353. 18:32really created a revolution in this
  354. 18:34extent because many companies are
  355. 18:36experimenting with prices all the time
  356. 18:38to try to figure out what demand is this
  357. 18:40is particularly common on eBay where
  358. 18:43sellers all the time are experimenting
  359. 18:45with the reserve price that they can
  360. 18:46charge on their
  361. 18:48auctions you know sometimes the same
  362. 18:50seller will sell the same good on a
  363. 18:52different day or even at the same time
  364. 18:55uh at different prices or different
  365. 18:57Reserve prices uh in order to tryy to
  366. 18:59see what demand is like now this is an
  367. 19:03auction yeah Christian sorry what's the
  368. 19:05reserve price uh a reserve price um is
  369. 19:11the lowest price that you'll accept
  370. 19:13without calling the auction off oh so
  371. 19:16it's like a starting price
  372. 19:18basically um now changing the reserve
  373. 19:22price uh is a lot like changing a price
  374. 19:25and it traces out something like a
  375. 19:26demand curve why why is that true what
  376. 19:29sort of demand curve could you create uh
  377. 19:32Evan using uh Reserve changing around
  378. 19:35the reserve price to affect uh prices
  379. 19:38and and the probability of sale so you
  380. 19:40want so you want me to explain why it
  381. 19:42would look like a demand or or what yeah
  382. 19:45how you know this is a starting price
  383. 19:47for an auction it's not like a price
  384. 19:49that I charge you know and the number of
  385. 19:52sales I get but you can get out of this
  386. 19:54something that's like a demand curve
  387. 19:55well instead of the number of sales you
  388. 19:58you could could look at for example the
  389. 20:00number of people who are going to be
  390. 20:01willing to bid or you could look at what
  391. 20:05kind of price of how much you can expect
  392. 20:07it to go up right or if it's going to or
  393. 20:10the or the probability of it um that's
  394. 20:13going to actually clear yeah so I think
  395. 20:16the easiest thing to correspond to is
  396. 20:18the probability that it actually clears
  397. 20:20right because if you set a higher
  398. 20:21reserve price the chance that it clears
  399. 20:23is going to be lower but what's the
  400. 20:25offsetting benefit you get when you set
  401. 20:26a higher reserve price you get more
  402. 20:28money why the reason why you get well I
  403. 20:32suppose it's that you're more likely to
  404. 20:35get to get more money right and the
  405. 20:36reason why is because let's suppose that
  406. 20:39you have one auction where you have the
  407. 20:41same item with a lower reserve price and
  408. 20:44you have for whatever reason one person
  409. 20:47who bids that Reser that lower reserve
  410. 20:49price in the first auction that's what
  411. 20:51you're going to get the second option if
  412. 20:53that person is still willing to pay
  413. 20:55higher then you then you get that money
  414. 20:57you can't get the lower exactly right so
  415. 20:59basically there are two circumstances
  416. 21:01where the reserve price matters one is
  417. 21:03one one in which if you'd set a lower
  418. 21:05reserve price someone would have bid
  419. 21:07above it but because you said a higher
  420. 21:09reserve price no one bids above it
  421. 21:12that's the case in which the reserve
  422. 21:13price deterred a sale from taking place
  423. 21:16on the other hand if you there's another
  424. 21:19circumstance which is that the um the
  425. 21:23low the second highest bid if there was
  426. 21:26one was below the reserve price that you
  427. 21:29set but um the highest bid was above it
  428. 21:32in that case it raises the price that
  429. 21:34you get um and so you can look at the
  430. 21:39average price that you get for a good as
  431. 21:41a function of your reserve price graphed
  432. 21:44against the um the probability of sale
  433. 21:48and those things will have a negative
  434. 21:49relationship the higher reserve price
  435. 21:50you set the higher average price you'll
  436. 21:52sell it at but also the lower will be
  437. 21:54the probability of sale and that'll
  438. 21:56Trace out something like a demand curve
  439. 21:57Yeah Austin this is not I guess strictly
  440. 22:00the same thing but I know on eBay
  441. 22:02typically they'll tell you whether the
  442. 22:03reserve price was met or not or not
  443. 22:05whereas like an art auctions and things
  444. 22:06it's typically private that don't tell
  445. 22:08you with the reserve do you get any like
  446. 22:10discontinuities related to that people
  447. 22:13you know just trying to barely clear it
  448. 22:14or
  449. 22:15something so people always barely I mean
  450. 22:18it's always people's incentive to First
  451. 22:20barely clear it uh in in the art
  452. 22:22auctions that incentive doesn't exist
  453. 22:24and a reserve price doesn't actually
  454. 22:25raise your Revenue all it does is stop
  455. 22:27the thing from being sold at a
  456. 22:29inefficiently low
  457. 22:31price
  458. 22:36um so yeah okay so uh luron inov uh
  459. 22:43Teresa coer John Levan uh and Neil
  460. 22:48sueras got all of eBay's
  461. 22:51data and they found 500,000 cases in
  462. 22:56which people had run experiment
  463. 22:59so you you guys probably know John list
  464. 23:02here runs lots of experiments
  465. 23:04right but um what they found was that um
  466. 23:11you don't just need to be an economist
  467. 23:13who goes out and runs experiments
  468. 23:15yourself sellers on eBay are running
  469. 23:18experiments all the time and so rather
  470. 23:20than running you know I don't know five
  471. 23:21or 10 experiments you could look at
  472. 23:23500,000 experiments by looking at what
  473. 23:26the sellers are choosing to do
  474. 23:27themselves
  475. 23:28and so um what they did is they looked
  476. 23:32at cases where the same seller sold the
  477. 23:34same item on slightly different terms
  478. 23:38either at the same time or at slightly
  479. 23:39different times and they use this to
  480. 23:41draw out demand curves for the auction
  481. 23:44just as I was describing and the
  482. 23:47interesting thing is they found that all
  483. 23:48these demand curves at a very similar
  484. 23:50shape yeah Evan so on eBay is there a
  485. 23:53penalty for listing the same item
  486. 23:54multiple times and then canceling the
  487. 23:56$999 they get the lowest price before
  488. 23:58they close oh I think there is yeah so
  489. 24:02you you have to agree to sell so then
  490. 24:04what so then what are they doing are
  491. 24:05these sellers who who have an inventory
  492. 24:08and then list the inventory I think
  493. 24:09that's the point they're trying to
  494. 24:10figure out what the market price should
  495. 24:12be by trying out different prices and
  496. 24:14then for the future yeah
  497. 24:17okay um so the interesting thing that
  498. 24:20they found is that marginal revenue is
  499. 24:22actually increasing in some parts
  500. 24:25um and so
  501. 24:29uh the cost if you think about it in
  502. 24:32this case is the value you could get by
  503. 24:35trying to sell that object again or
  504. 24:36keeping it yourself right and there's a
  505. 24:39possibility of there being multiple
  506. 24:40intersections between marginal cost
  507. 24:42which is constant as a function of the
  508. 24:44probability right it's just the value of
  509. 24:46that good and the average and the uh
  510. 24:50marginal
  511. 24:51revenue okay so let me show you a
  512. 24:53picture of this and show you what we do
  513. 24:55to analyze these cases so here's what
  514. 24:57they found they found that for tons of
  515. 24:59different Goods if we divided the uh
  516. 25:03price of the Good by the um assessed
  517. 25:08value that um the demand curves looked
  518. 25:13very similar to one another and they
  519. 25:15looked like this they were sort of
  520. 25:18reasonably sloped here but then they get
  521. 25:20incredibly flat as you get out to high
  522. 25:22probabilities why is that well as a
  523. 25:26object is getting down to a low low
  524. 25:28probability of sorry a low price there's
  525. 25:31always going to be someone on eBay who's
  526. 25:33just looking for deals who's going to
  527. 25:36snap that thing up and go resell it
  528. 25:38right and so that makes demand really
  529. 25:41have a very sharp floor underneath it
  530. 25:45these people up here are people who are
  531. 25:46actually going to keep that good these
  532. 25:48people down here are people are just
  533. 25:49going to go and resell it again right um
  534. 25:54and uh you can fit a curve through this
  535. 25:58you can just you know use a polinomial
  536. 26:00fit on Excel and you can fit a third
  537. 26:02degree polinomial through this and you
  538. 26:04get a marginal revenue curve that is not
  539. 26:07just decreasing like all those marginal
  540. 26:09revenue curves we looked at before which
  541. 26:11means that if you had a marginal cost
  542. 26:13that was right here there would be three
  543. 26:15intersections between marginal cost uh
  544. 26:18and
  545. 26:19demand now does anyone want to guess
  546. 26:22imagine that marginal cost were here
  547. 26:26which point of these three would
  548. 26:28actually be the optimal quantity for you
  549. 26:30to
  550. 26:31sell the optimal probability with which
  551. 26:34a sale would
  552. 26:39occur marinal cost this way again sorry
  553. 26:42marginal cost let's say it's at 75 so
  554. 26:47it's just below that black line
  555. 26:54I what do you think so is the area like
  556. 26:56of those two little regions like the
  557. 27:00yeah between the pink and the black line
  558. 27:01are those equal yes that's the point but
  559. 27:04you have to figure out why that's the
  560. 27:05case that's what I'm trying to take you
  561. 27:07guys through
  562. 27:15now well notice that the profits that a
  563. 27:18firm earns is the area between the
  564. 27:20marginal revenue curve and the um
  565. 27:24marginal cost curve up to the point that
  566. 27:27they go to so if the firm produces here
  567. 27:30they get all this area and profits but
  568. 27:32they don't get anything over here if
  569. 27:34they produce over here they're going to
  570. 27:36actually take losses in this region down
  571. 27:38here and then they'll make gains over
  572. 27:41here but the gains are bigger than the
  573. 27:43losses here right the area above is
  574. 27:45bigger than the area below and so
  575. 27:47they'll produce over here on the other
  576. 27:50hand if they had a cost that was 85 like
  577. 27:53up here then if they produced over here
  578. 27:56they'd take losses over this full region
  579. 27:58here and only make gains over here which
  580. 28:00would not be worth it so they'd be
  581. 28:02better off producing over here so this
  582. 28:05line which is called the ironing line is
  583. 28:07a line where area above the line and
  584. 28:09below the curve equals the area below
  585. 28:11the line and above the curve and that is
  586. 28:15exactly the cost at which they would
  587. 28:18jump from producing from selling with
  588. 28:21this probability to selling with this
  589. 28:23probability so if the co if someone's
  590. 28:26cost went from you know know 79 to 82
  591. 28:31you would see the price jump from on
  592. 28:34average from about what is this
  593. 28:3882 up
  594. 28:40to uh
  595. 28:431.05 right so there would be a
  596. 28:45discontinuous change in price when there
  597. 28:47was a continuous change in the cost and
  598. 28:50the reason is that you're basically
  599. 28:53making a decision of which of two
  600. 28:54markets to serve are you going to try to
  601. 28:57just give this to the resellers and let
  602. 28:59them resell it in which case you'll set
  603. 29:00basically a zero reserve price or are
  604. 29:03you going to try to really sell this to
  605. 29:07a final consumer only in which case
  606. 29:09you'll probably set a reserve price
  607. 29:10that's about equal to its value does
  608. 29:12that make
  609. 29:14sense so this technique ironing is a
  610. 29:17more General technique you can use
  611. 29:18anytime you have a
  612. 29:20non-monotonic uh marginal revenue curve
  613. 29:22or really non-monotonic anything
  614. 29:24function that you have to optimize in
  615. 29:25economics you can always replace it with
  616. 29:27a mon iic one by using ironing
  617. 29:30procedures like this canceling out the
  618. 29:32area above and below
  619. 29:35yeah the IR line was determined by like
  620. 29:39who wants to resell wants to keep it
  621. 29:41finally you just talk a little more
  622. 29:43about well so I mean this is just a
  623. 29:45hypothesis but the reason these demand
  624. 29:47curves look they have this shape where
  625. 29:49they're like quite steeply decreasing
  626. 29:52and then you get out to about a0 five
  627. 29:54probability of sale and they're almost
  628. 29:56totally flat after that and the reason I
  629. 29:58think is that basically the people who
  630. 30:01are buying it and showing up with about5
  631. 30:05probability are people who actually want
  632. 30:06to keep that thing
  633. 30:08forever and they have like a decreasing
  634. 30:10demand curve but people who just want to
  635. 30:12resell it their value is completely
  636. 30:14constant because they all just have the
  637. 30:15same cost of reselling it
  638. 30:20right
  639. 30:22okay so Monopoly is two basic welfare
  640. 30:26related effects compared to
  641. 30:28competition the first is that it
  642. 30:31transfers resources um to the
  643. 30:35monopolist
  644. 30:38um from uh the consumers and the second
  645. 30:41is it inefficiently reduces the output
  646. 30:44in the
  647. 30:45industry so how do we know Mike fosco
  648. 30:49how do we know that this reduction in
  649. 30:51quantity is socially inefficient uh from
  650. 30:53the dead rate loss we're um the they're
  651. 30:56not producing uh Aral cost is equal to
  652. 30:59the price they're doing less than that
  653. 31:02okay so why does that create dead weight
  654. 31:03loss because there are more gains to be
  655. 31:06made for society in general if you
  656. 31:08produce more output um because then the
  657. 31:10benefit to the consumer is greater than
  658. 31:12the uh
  659. 31:15lower Yeah so basically this is a case
  660. 31:18in which at Price equals marginal cost
  661. 31:21the value the consumer gets is exactly
  662. 31:24equal to the cost of the firm of
  663. 31:26producing if the price is above the
  664. 31:28marginal cost the consumer gets a
  665. 31:29greater value out of the product than
  666. 31:31the than the cost of producing it and
  667. 31:34therefore it would be socially valuable
  668. 31:35to produce more of it and the firm is
  669. 31:38eliminating some sales that would be
  670. 31:40beneficial because the benefit to the
  671. 31:43consumers would be greater than the cost
  672. 31:46okay
  673. 31:48um now uh the inefficiency of Monopoly I
  674. 31:53think is quite apparent in real life
  675. 31:56it's the reason why information Goods
  676. 31:57like music aren't freely available right
  677. 32:01it's the reason why there are empty
  678. 32:02parking lots in busy cities uh that
  679. 32:07charge High rates right like it's
  680. 32:09completely crazy for there to be parking
  681. 32:11lots that are empty and people who are
  682. 32:13roaming around the streets looking for
  683. 32:15places to park right because there's no
  684. 32:17cost of have on the margin of putting
  685. 32:19one more person into that parking lot
  686. 32:21and there's a big uh cost of having them
  687. 32:24roaming around the streets right
  688. 32:28uh yeah Evan couldn't you see the high
  689. 32:30parking rates as as just a fee of the
  690. 32:34people who are going to park in that
  691. 32:36area are paying to increase the
  692. 32:38probability there is a
  693. 32:39spot because I'm from one of those very
  694. 32:41crowded areas and it's not normally the
  695. 32:43case people are driving around because
  696. 32:46there's not a spot in the parking lots
  697. 32:47because even with high prices it's
  698. 32:49usually
  699. 32:49full really I don't think that that's
  700. 32:52true I don't think it's usually true
  701. 32:54that parking lots usually have a fair
  702. 32:56number of vacancies in in almost all
  703. 32:59times of the day I mean there's a few
  704. 33:00parking lots that fill up at a few times
  705. 33:02of the day but it's very rarely the case
  706. 33:04that all the parking lots are actually
  707. 33:06full so uh yeah Austin are parking lots
  708. 33:10really monopolies though I mean I feel
  709. 33:12like for parking lots at least it's more
  710. 33:14of the case where it's yeah so that's a
  711. 33:15good question I don't think that
  712. 33:17structurally they're monopolies but I
  713. 33:19think it's basically they are monopolies
  714. 33:21because once you've turn you can't
  715. 33:22figure out what the price of the parking
  716. 33:24lot is until you've already turned into
  717. 33:26the parking lot and then I mean in other
  718. 33:28words like people have to invest like
  719. 33:30resources to learn the prices of the
  720. 33:32parking lot if there was complete price
  721. 33:34transparency I think it would
  722. 33:35effectively be perfect competition and I
  723. 33:37think that's starting to happen because
  724. 33:39of this app best parking I don't know if
  725. 33:41you guys have this I love this app and
  726. 33:43it like tells you the rates of all the
  727. 33:44parking lots and I think if everyone
  728. 33:46comes to have that app then there will
  729. 33:47be perfect competition but I think that
  730. 33:49not everybody has it yet and so there is
  731. 33:51effectively Monopoly are there any
  732. 33:52dynamically priced parking lots in
  733. 33:55Chicago well I mean there's almost all
  734. 33:57almost all parking lots have some amount
  735. 33:58of dynamic pricing they all have like
  736. 34:00you know special deals but not really
  737. 34:03intelligently dynamically priced ones no
  738. 34:06I mean they're like the way they
  739. 34:07dynamically price is better than none
  740. 34:09but it's not as intelligent as you could
  741. 34:10with a really adaptive system but to
  742. 34:12really make something like that work
  743. 34:13You' need price transparency on that as
  744. 34:15well so you'd need to have like the app
  745. 34:17linked to the prices and people would
  746. 34:20have to like have their apps telling
  747. 34:22them which lot to go to based on its
  748. 34:24current you know occupancy and your for
  749. 34:27a price I think I read San Francisco's
  750. 34:28doing that now yeah I think cities in
  751. 34:31California are trying that 100 yeah what
  752. 34:33what what things isn't California doing
  753. 34:35better than the rest of the world I mean
  754. 34:38I'm a Californian
  755. 34:41um um okay so
  756. 34:45effectively Monopoly means that
  757. 34:48consumers have an externality on the
  758. 34:52firm because if they purchase more the
  759. 34:54firm is going to make more profits
  760. 34:55because the firm is earning a markup
  761. 34:57over marginal cost on every unit that it
  762. 34:59sells and these extra profits that are
  763. 35:02created are not mediated through the
  764. 35:03price system so there are real
  765. 35:05externality and they suggest a standard
  766. 35:08pigouvian Solutions like subsidizing
  767. 35:10purchases of the goods by consumers or
  768. 35:13perhaps regulating the firm's price down
  769. 35:15to cost or mandating an efficient
  770. 35:18quantity uh to be produced and we're
  771. 35:20going to talk about some of these
  772. 35:22policies in practice on Thursday but
  773. 35:24they're far less common that you'd think
  774. 35:27and in lect 13 we're going to talk a
  775. 35:28little bit about why despite the
  776. 35:30ubiquity of Market power we don't have
  777. 35:32solutions that really uh address them
  778. 35:35that that often now you know another
  779. 35:38thing to keep in mind is that there are
  780. 35:40other solutions that you could use to
  781. 35:42address Market power which maybe are
  782. 35:45seem a little bit more dirty uh or less
  783. 35:49clearly cleanly lined up with economics
  784. 35:51but are you know from a social
  785. 35:53perspective just as valuable so for
  786. 35:55example advertising or creating Prestige
  787. 35:59for products can make people value them
  788. 36:03more and that can cause consumers to buy
  789. 36:08at prices that are above what they're
  790. 36:09willing to pay and therefore offset the
  791. 36:12Distortion associated with Monopoly so
  792. 36:14some sort of deceptive advertising or
  793. 36:17building hyper on a product might
  794. 36:18actually be socially beneficial because
  795. 36:20it offsets the Monopoly
  796. 36:23Distortion we consider that paying more
  797. 36:25than the what like that's considered
  798. 36:28paying more than their willing well I
  799. 36:29mean imagine you like a lot of people
  800. 36:31say oh they trick you into making you
  801. 36:32feel like you want the product when you
  802. 36:34don't really want it or you're willing
  803. 36:35to pay more than you're really willing
  804. 36:37to pay but that could actually be good
  805. 36:38in the context of a monopolized product
  806. 36:40because otherwise it would be
  807. 36:40inefficiently
  808. 36:42underconsumed uh yeah but like in that
  809. 36:44scenario though um although you'd be
  810. 36:46producing the right output like the
  811. 36:47right right quantity like the benefit
  812. 36:50would be transferred from like conser to
  813. 36:52the yeah that's true okay so but still
  814. 36:56from a social perspective
  815. 36:58in in aggregate it's still value and in
  816. 37:00fact it might even be good to transfer
  817. 37:01to the firm if the firm innovated in
  818. 37:03order to create that product because
  819. 37:06that gives more incentives for
  820. 37:07Innovation yeah Evan why is it that the
  821. 37:09soci social socially optimal quantity
  822. 37:12hasn't changed in response to the
  823. 37:14advertising because if now you change
  824. 37:15how people value it why well I mean it
  825. 37:17all depends how you think about
  826. 37:18advertising but some people think about
  827. 37:20advertising as sort of deceptive and
  828. 37:22making you feel like you want something
  829. 37:23more than you really want it and that
  830. 37:25wouldn't change the socially optimal
  831. 37:26quantity so you're saying that if you
  832. 37:28think of it there's like still a
  833. 37:30constant real want yeah so there there's
  834. 37:33a paper by Dixit and nor uh and Norman
  835. 37:37which is all about that uh yeah if we
  836. 37:40assume that people have a constant real
  837. 37:43want then uh be being able to
  838. 37:47deceptively advertise
  839. 37:50essentially someone allow it allows the
  840. 37:53monopolist to appropriate some money
  841. 37:56that
  842. 37:59is uh that consumers really aren't
  843. 38:02willing to pay so might it create too
  844. 38:04much incentive yeah so you'll typically
  845. 38:07want like you'll spend too much on
  846. 38:08Advertising but it will also typically
  847. 38:10be bad if you don't allow advertising at
  848. 38:15all
  849. 38:16so okay so the debt the like any tax or
  850. 38:20externality the value of extra
  851. 38:23production will be equal to the wedge
  852. 38:25the sort of like uh uh difference
  853. 38:28between price and marginal cost times
  854. 38:30the change in quantity uh that occurs
  855. 38:32when when something changes yeah ver um
  856. 38:35so even though that like allocates like
  857. 38:38a socially optimal level uh does it
  858. 38:40still create like negative externality
  859. 38:43because um consumers buy more than like
  860. 38:45they so advertising will have a negative
  861. 38:47externality because you'll be taking
  862. 38:49money from consumers and giving it to
  863. 38:50the firm and it's an action taken by the
  864. 38:52firm so it does have a negative
  865. 38:54externality but on the other hand it
  866. 38:56might be more efficient then completely
  867. 38:58Banning that activity so you might want
  868. 38:59to tax advertising but you wouldn't want
  869. 39:01to eliminate it
  870. 39:03entirely um yeah Christian so would that
  871. 39:05be a real externality of advertising
  872. 39:08yeah can you it's real because it affect
  873. 39:13it hurts the consumers but doesn't
  874. 39:15benefit anyone other than the firm and
  875. 39:17so the firm's the one
  876. 39:22doing okay um so as a result we can
  877. 39:27measure
  878. 39:28the dead weight loss using the standard
  879. 39:30dead weight loss triangle the only
  880. 39:32difference is now the size of this
  881. 39:34triangle is determined by the Monopoly
  882. 39:36Optimum and in particular it has a
  883. 39:38particular relationship to Monopoly
  884. 39:40profits that we'll explore in a minute
  885. 39:42and this is the triangle bounded by the
  886. 39:44supply curve the demand curve and the
  887. 39:45equilibrium quantity now we can measure
  888. 39:48Monopoly profits graphically in two ways
  889. 39:51one is the area between the equilibrium
  890. 39:53price and marginal cost or the area
  891. 39:56between marginal revenue and marginal
  892. 39:58cost so let me show you that so the area
  893. 40:02between price so if this is the marginal
  894. 40:05cost curve and this is the marginal
  895. 40:08revenue curve here is the price and
  896. 40:12profits are either the area between this
  897. 40:14price and marginal cost C plus d or the
  898. 40:17area between uh marginal revenue and
  899. 40:20marginal cost which is a plus c and you
  900. 40:23notice by similar triangles these are
  901. 40:24the same areas wait which which what
  902. 40:27what what each l so this is the demand
  903. 40:30this is the marginal revenue this is the
  904. 40:32marginal cost so this is the optimal
  905. 40:35quantity and the optimal price so here's
  906. 40:38profit the area between price and
  907. 40:40marginal cost or profit the area between
  908. 40:43marginal revenue and marginal cost and
  909. 40:45they're the same by similar
  910. 40:48triangles we can also measure consumer
  911. 40:50surplus is either the demand between the
  912. 40:53area between demand and price that's the
  913. 40:55way we usually measure it that's a plus
  914. 40:57be up here right but you can also
  915. 41:00measure it as the area between demand
  916. 41:02and the marginal revenue curve because
  917. 41:04remember that the difference between de
  918. 41:06uh demanded marginal revenue is the uh
  919. 41:08marginal surplus of those consumers so
  920. 41:11it's the area B plus d which Again by
  921. 41:13similar triangles is the same as the
  922. 41:15area a plus
  923. 41:17b
  924. 41:19okay
  925. 41:22um so
  926. 41:26um the dead weight loss
  927. 41:29triangle is
  928. 41:31e the area over here because this would
  929. 41:35have been the efficient quantity and
  930. 41:37here's all the loss in willingness to
  931. 41:39pay minus marginal cost that occurs
  932. 41:41between
  933. 41:42those
  934. 41:44okay now um Alfred Marshall who is uh
  935. 41:48not only one of the you know most famous
  936. 41:51economists of all time but also was um
  937. 41:57sort of the founder of price Theory
  938. 41:59which is the school of Economics that
  939. 42:01The Chicago School uh is so into um said
  940. 42:06that you can think about almost
  941. 42:08everything in economics in terms of tax
  942. 42:11incidents and you probably learned in
  943. 42:13both your basic courses and probably
  944. 42:14last term the basic principles of tax
  945. 42:17incidence for uh perfect competition and
  946. 42:20use those to think about all sorts of
  947. 42:22different types of interventions uh that
  948. 42:25happened in markets
  949. 42:28now most of what's different under
  950. 42:30Monopoly remember that Monopoly models
  951. 42:32are really only useful for thinking
  952. 42:33about interventions that occur directly
  953. 42:35through the actions of that firm and so
  954. 42:38if we just think about the incidence of
  955. 42:40changes to that firm we can think about
  956. 42:42most interventions that are relevant to
  957. 42:44Monopoly so I want to give a brief recap
  958. 42:47of compet perfectly competitive
  959. 42:48incidents and then I want to contrast
  960. 42:50that to
  961. 42:51monopo and um Evan could you tell us
  962. 42:55some of the principles of incidence
  963. 42:57under perfect
  964. 42:59competition um
  965. 43:03princip incidence of
  966. 43:15taxes can't remember
  967. 43:17it um anybody else want to yeah Phil um
  968. 43:22in the short run uh because
  969. 43:28well in the long run the incidence is
  970. 43:30purely on consumers because a firms need
  971. 43:35to enter and exit to maintain zero
  972. 43:38profits in equilibrium well if in the
  973. 43:40long run the demand the supply curve is
  974. 43:42extremely elastic and the demand curve
  975. 43:44is not so elastic but yeah um yeah
  976. 43:48assuming assuming infinite using that a
  977. 43:52standard
  978. 43:53elasticity yeah but I mean even more
  979. 43:56basic than than that
  980. 43:58uh tavish whoever has the more
  981. 44:02elastic
  982. 44:05supp yeah that's the most that's one of
  983. 44:07the most basic principles so the most
  984. 44:09basic principle is that the physical
  985. 44:11incidents who literally pays the tax is
  986. 44:14irrelevant to who actually Bears the
  987. 44:17burden of the tax because if we charge
  988. 44:20tax on the consumers the price of the
  989. 44:22good will fall if we charge tax on the
  990. 44:25producers the price of the good will R
  991. 44:27in response to that most likely right
  992. 44:30and um therefore we can always treat the
  993. 44:33tax as if it's directly paid by the
  994. 44:35producers and then just study how it
  995. 44:37gets passed through to Consumers and I'm
  996. 44:40going to call that rate of pass through
  997. 44:41the rate at which the price increases
  998. 44:42when the tax increases uh
  999. 44:45dpdt uh the pass through rate
  1000. 44:48row so then the fraction of the tax that
  1001. 44:54ends up getting paid by the
  1002. 44:55consumers uh is going to be equal to the
  1003. 44:58pass through rate and the fraction
  1004. 44:59that's paid by the producers is 1 minus
  1005. 45:01the pass through rate right and all of
  1006. 45:05the tax is borne by one side or the
  1007. 45:07other right if we have put in a small
  1008. 45:10tax all of that tax is born either by
  1009. 45:13the consumers or the producers so if we
  1010. 45:16want to call the incidence the ratio of
  1011. 45:18the amount borne by the consumers to the
  1012. 45:20amount born by the producers that will
  1013. 45:22be row over 1 minus
  1014. 45:24row okay so the second principle and
  1015. 45:27this is what tavish was getting at is
  1016. 45:30that the inelastic side of the market
  1017. 45:32Bears the um tax uh in particular the
  1018. 45:36pass through rate is equal to 1 over 1
  1019. 45:38plus the elasticity of demand over the
  1020. 45:40elasticity of supply and Tanner could
  1021. 45:44you derive that
  1022. 45:46formula you'll probably want to do it on
  1023. 45:48the board yeah sure
  1024. 46:09can I ER yeah please uh there's there's
  1025. 46:11a eraser if you want it where's
  1026. 46:23that so I'm driving the uh the price one
  1027. 46:26over 1 plus the man Supply right yeah
  1028. 46:34okay it's the pass through is equal to
  1029. 46:36one oh pass yeah yeah sorry so to derive
  1030. 46:39the pass through rate remember you need
  1031. 46:41to do a comparative static it's how does
  1032. 46:43the price change when the tax changes
  1033. 46:45right so what's the equilibrium
  1034. 46:47conditions in the market
  1035. 46:50um just it's demand equals Supply right
  1036. 46:54but remember that the producer doesn't
  1037. 46:56get the full price he only gets the
  1038. 46:57price minus the tax so how would you set
  1039. 46:59up the equilibrium conditions for
  1040. 47:02that let's see
  1041. 47:20so we want to find the change in price
  1042. 47:23as the as the tax the change change in
  1043. 47:25price of the tax happens yeah so what's
  1044. 47:27the first just write down the
  1045. 47:29equilibrium condition so demand is a
  1046. 47:32function of
  1047. 47:41price just D of P right that's just a
  1048. 47:43function D of P or D of P like demand of
  1049. 47:49price is equal to the supply is a
  1050. 47:51function of price minus the tax right
  1051. 47:56right yeah okay so now how would you
  1052. 47:59figure out how the price changes with
  1053. 48:01respect to the
  1054. 48:02tax uh take size
  1055. 48:13yeah so by the implicit function theorem
  1056. 48:15you have to put dpdt here and you have
  1057. 48:18to put dpdt minus1 there
  1058. 48:28yeah you heard parentheses I know okay
  1059. 48:32so now you need to solve for dpdt which
  1060. 48:33is the pass through r
  1061. 49:22good
  1062. 49:29you can drop the arguments inside of
  1063. 49:30those things it'll make your life
  1064. 49:37easier right okay and then try dividing
  1065. 49:41through both the top and the Bottom by S
  1066. 49:45Prime by S Prime
  1067. 49:54yeah no don't don't divide both sides
  1068. 49:58just divide the top and the bottom of
  1069. 49:59this expression
  1070. 50:07by yeah D Prime over S
  1071. 50:11Prime yeah you go to a negative there
  1072. 50:14this but and put a negative in Fr of
  1073. 50:17this
  1074. 50:18yeah
  1075. 50:20um yeah and then note that D Prime over
  1076. 50:25S Prime is equal to the e of demand over
  1077. 50:27the elasticity of supply because both
  1078. 50:29have the same price and the same
  1079. 50:31quantity right at equilibrium and so
  1080. 50:35that's how you get this
  1081. 50:37formula heroic job Tanner thank you um
  1082. 50:41okay so just to give you an intuitive
  1083. 50:43sense for this suppose that um the
  1084. 50:47demand curve is totally inelastic and
  1085. 50:49the supply curve is somewhat elastic
  1086. 50:51then look the consumers are going to
  1087. 50:53Bear all of the tax if we put the tax on
  1088. 50:56the price price Rises exactly by the
  1089. 50:57amount of the tax and the consumers bear
  1090. 51:00it
  1091. 51:01all um on the other hand if the supply
  1092. 51:05is perfectly elastic and then when the
  1093. 51:09um demand is perfectly elastic then when
  1094. 51:12the supply uh when the tax Rises the um
  1095. 51:17price is going
  1096. 51:19to
  1097. 51:21uh then the price is going to stay the
  1098. 51:24same and the amount received by the the
  1099. 51:26firm is going to fall by exactly the
  1100. 51:28amount of the tax and therefore the firm
  1101. 51:30will bear all the incidents right now
  1102. 51:33more generally if both are elastic it
  1103. 51:36depends on the relative elasticity of
  1104. 51:38the two curves um as shown here
  1105. 51:43okay now if we keep raising the tax on a
  1106. 51:46market if we start with a small amount
  1107. 51:49and we raise it f higher and higher at
  1108. 51:51some point we're going to reach a tax
  1109. 51:53that's so high that no one's willing to
  1110. 51:55buy the product at all anymore more
  1111. 51:57right and we can work backwards from
  1112. 51:59that point to determine the total amount
  1113. 52:01of consumer surplus right so because
  1114. 52:04once we reach a tax of T there's no
  1115. 52:06consumer surplus the consumer surplus is
  1116. 52:09just going to be the integral of the
  1117. 52:11pass through rate times the quantity
  1118. 52:13because that's how much the consumers
  1119. 52:15lose every time we raise the price by a
  1120. 52:17little by the tax by a little bit and
  1121. 52:20the producer Surplus is going to be the
  1122. 52:22integral of one minus the pass through
  1123. 52:24rate times the quantity so if we then
  1124. 52:26let the average pass through rate be the
  1125. 52:28quantity weighted average of pass
  1126. 52:30through between a tax of zero and the
  1127. 52:34maximum tax then the global incidence
  1128. 52:38the ratio of total consumer to Total
  1129. 52:40producer Surplus is the ratio of the
  1130. 52:42average pass through over one minus the
  1131. 52:44average pass through right so you know
  1132. 52:49often when you say the consumer Bears
  1133. 52:51the weight of a tax you want to think oh
  1134. 52:55poor consumer he has to pay all the tax
  1135. 52:58but in reality the only reason the
  1136. 52:59consumer is bearing the weight of the
  1137. 53:00tax is that the consumer is the one who
  1138. 53:02benefits from the market existing in the
  1139. 53:04first place right the person who Bears
  1140. 53:07the tax is the person who benefits from
  1141. 53:08the market being there right um so the
  1142. 53:14global ratio of consumer to producer
  1143. 53:16Surplus is just the uh quantity weighted
  1144. 53:21average of the ratio that happens for a
  1145. 53:24small change in the tax rate
  1146. 53:28so the inelastic side is the one that
  1147. 53:30benefits from the market existing
  1148. 53:32they're the ones who really need it to
  1149. 53:33be there whereas the elastic side
  1150. 53:35doesn't care whether the Market's there
  1151. 53:37or not they're H just as happy either
  1152. 53:38way
  1153. 53:43okay now um under Monopoly there's going
  1154. 53:47to be a fundamentally uh there incidence
  1155. 53:51is going to be fundamentally different
  1156. 53:52in a couple of ways so it's still going
  1157. 53:55to be the case that physical and
  1158. 53:58economic incidents are independent of
  1159. 54:00one another um because it doesn't matter
  1160. 54:03whether you tax the consumer or the
  1161. 54:05producer but now rather than the tax
  1162. 54:07being split between the two sides
  1163. 54:10there's actually going to be an excess
  1164. 54:12burden because too little of the good is
  1165. 54:14already being produced there's going to
  1166. 54:17be more loss to the firm and the
  1167. 54:20consumer than is uh the revenue that the
  1168. 54:23government
  1169. 54:24gets um
  1170. 54:27in particular The Firm chooses its
  1171. 54:30quantity so as to maximize prices and
  1172. 54:33its profits are given by this formula so
  1173. 54:36what is going to be the loss to the firm
  1174. 54:38when the taxes increase by a little bit
  1175. 54:41uh reishi and you can use the envelope
  1176. 54:43theorem uh see if you can use the no no
  1177. 54:46don't look uh see if you can use the
  1178. 54:48envelope theorem to figure out really
  1179. 54:51simply uh what the effect of a change in
  1180. 54:53the tax is on the firm's profits in this
  1181. 54:57okay
  1182. 55:03um remember the quantity is being chosen
  1183. 55:06optimally right
  1184. 55:11right the tax changes by a very small
  1185. 55:15amount
  1186. 55:18the quantity
  1187. 55:21also the quty also Chang
  1188. 55:23by that's true but it's not enough what
  1189. 55:28does the envelope theorem tell us to
  1190. 55:30do to differentiate with respect respect
  1191. 55:37Quan yeah it says that we can hold fixed
  1192. 55:41anything that's being
  1193. 55:42optimized right when we take the
  1194. 55:44derivative of the thing that it's
  1195. 55:46optimizing right so here what that what
  1196. 55:48would that tell us the effect of the tax
  1197. 55:50on profits is um you can hold profits
  1198. 55:55you can hold quantity
  1199. 55:56that's the thing you're choosing to
  1200. 55:59optim
  1201. 56:01so would it just
  1202. 56:05be quantity F would just be the um the
  1203. 56:10Der with respect
  1204. 56:15to T directly right so just be um
  1205. 56:21negative uh just Q minus just negative
  1206. 56:26Q yeah so the monopolist because he
  1207. 56:29chooses his quantity to maximize profits
  1208. 56:33um Bears the full burden of the
  1209. 56:38tax he gets exactly negative Q that's
  1210. 56:41the full amount of Revenue raised right
  1211. 56:43and he Bears all of that directly right
  1212. 56:47but the consumer still loses the pass
  1213. 56:51through rate times the quantity right
  1214. 56:53because if this price Rises he's worse
  1215. 56:55off and it will will typically rise
  1216. 56:57right so the excess burden then is row *
  1217. 57:02Q so everything the burden is fully
  1218. 57:05borne by the monopolist and then it's
  1219. 57:07additionally borne as excess burden by
  1220. 57:09the
  1221. 57:10consumer therefore the incidence the
  1222. 57:12ratio of how much the consumer loses to
  1223. 57:14how much the firm loses is the pass
  1224. 57:16through rate divided by one or just the
  1225. 57:18pass through rate right and again we can
  1226. 57:20integrate this up as before to get the
  1227. 57:22ratio of consumer to producer Surplus is
  1228. 57:24the average pass through rate
  1229. 57:28okay so just to see how this works
  1230. 57:31here's a monopolist here's his marginal
  1231. 57:33cost imagine now we shift up his
  1232. 57:34marginal cost with a
  1233. 57:36tax how much does he lose in profits
  1234. 57:39well profits is the area between
  1235. 57:40marginal revenue and marginal cost and
  1236. 57:44that's Fallen by the quantity multiplied
  1237. 57:47by the change right now there's a little
  1238. 57:51extra triangle here but that's very
  1239. 57:53small that's second order
  1240. 57:56okay so um under uh under Monopoly the
  1241. 58:03logic of incidence is therefore
  1242. 58:05different in two ways so one is that
  1243. 58:07there's this extra dead weight loss so
  1244. 58:09that the incidence is not just split but
  1245. 58:11there's this excess burden and the
  1246. 58:13second thing is that the marginal
  1247. 58:15revenue curve and not just the demand
  1248. 58:17curve will help determine the pass
  1249. 58:19through rate so now I want to consider
  1250. 58:22uh P the pass through rate so Tanner
  1251. 58:25very nice nicely derived from us for us
  1252. 58:27the pass through rate under perfect
  1253. 58:29competition let's do the same thing for
  1254. 58:31Monopoly right for Monopoly marginal
  1255. 58:33revenue is equal to marginal cost which
  1256. 58:35also includes the tax so implicitly
  1257. 58:38differentiating we get that marginal
  1258. 58:39revenue Prime multiplied by the
  1259. 58:42derivative of quantity with respect to
  1260. 58:43the tax is equal to marginal cost Prime
  1261. 58:46Times the derivative of quantity with
  1262. 58:47respect to the tax plus
  1263. 58:51one um and the derivative of quantity
  1264. 58:55with respect to the tax is therefore
  1265. 58:57equal to one over the derivative of
  1266. 58:59marginal revenue minus the derivative of
  1267. 59:01marginal
  1268. 59:04cost um now how much does that lead to a
  1269. 59:07change in price well how much does price
  1270. 59:10change when quantity changes well it's
  1271. 59:11just the derivative of price with
  1272. 59:13respect to quantity and so the passive
  1273. 59:15rate is p Prime over Mr Prime minus MC
  1274. 59:19Prime now remember that Mr is equal to p
  1275. 59:22+ P Prime * Q so if we let the marginal
  1276. 59:26Surplus as we were talking about before
  1277. 59:28equal to P Prime *
  1278. 59:31q and we identify the marginal cost
  1279. 59:34curve remember that the supply curve is
  1280. 59:36just the inverse of the marginal cost
  1281. 59:37curve so we can identify the supply
  1282. 59:39curve with marginal cost
  1283. 59:41curve then marginal cost Prime is equal
  1284. 59:44to P over Q * the elasticity of supply
  1285. 59:49just by the same logic we did to derive
  1286. 59:52the elasticity of uh demand in the
  1287. 59:55learner index before and P Prime is
  1288. 59:57equal to P Q * elasticity of demand then
  1289. 1:00:01we can replace all these terms with
  1290. 1:00:03these
  1291. 1:00:04here and we can divide through to give
  1292. 1:00:07that the pass through rate is equal to 1
  1293. 1:00:09over 1 plus the elasticity of demand
  1294. 1:00:12minus one / the elasticity of supply
  1295. 1:00:15Plus the one over the elasticity of the
  1296. 1:00:17marginal Surplus function now this is
  1297. 1:00:20basically similar to what we saw before
  1298. 1:00:22right there's still 1 plus the
  1299. 1:00:24elasticity of demand divided by the El
  1300. 1:00:25elasticity of supply there's a negative
  1301. 1:00:27one in here which is not all that
  1302. 1:00:29important but the key new term is the
  1303. 1:00:32one over the elasticity of the marginal
  1304. 1:00:34Surplus
  1305. 1:00:36function so the question is how should
  1306. 1:00:38we interpret this elasticity of the
  1307. 1:00:40marginal Surplus function Kim do you
  1308. 1:00:42have any thoughts about
  1309. 1:00:46that
  1310. 1:00:49yeah anybody else like we we saw how the
  1311. 1:00:53marginal Surplus function was behaving
  1312. 1:00:55before
  1313. 1:00:56right it was that area between the
  1314. 1:00:58demand and the marginal revenue and we
  1315. 1:01:00saw that it was doing different things
  1316. 1:01:02depending on the demand curve that we
  1317. 1:01:04looked
  1318. 1:01:17at well so the El one over the
  1319. 1:01:20elasticity of the marginal Surplus
  1320. 1:01:23measures the curvature of
  1321. 1:01:27demand it's going to be greater than one
  1322. 1:01:32for concave demand how do we know that
  1323. 1:01:34well remember as quantity was increasing
  1324. 1:01:36that thing that that distance was
  1325. 1:01:38increasing more than one for one when
  1326. 1:01:41you had concave demand it wasn't just
  1327. 1:01:43linearly increasing it was increasing at
  1328. 1:01:46an increasing rate so that means it had
  1329. 1:01:47an elasticity greater than one with
  1330. 1:01:49linear demand it was increasing at a
  1331. 1:01:51constant rate so that means it had an
  1332. 1:01:53elasticity of one
  1333. 1:01:55and for negative exponential demand it
  1334. 1:01:57was completely constant so that mean it
  1335. 1:01:59had zero elasticity right for log convex
  1336. 1:02:03demands like the um the
  1337. 1:02:07marginal uh like the constant elasticity
  1338. 1:02:10demand it was it was actually decreasing
  1339. 1:02:12and that means it has a negative
  1340. 1:02:13elasticity right and if this is negative
  1341. 1:02:17enough then the passor rate can even be
  1342. 1:02:20infinite uh how do we know that well
  1343. 1:02:23remember that in the inov at all example
  1344. 1:02:27right we had that ironing line so that a
  1345. 1:02:28small increase in marginal cost could
  1346. 1:02:30lead to a discontinuous increase in
  1347. 1:02:32price that's an infinite pass through
  1348. 1:02:34rate and that came from the fact that
  1349. 1:02:35that marginal Surplus was
  1350. 1:02:38shrinking uh very quickly as the
  1351. 1:02:42quantity was increasing right so in
  1352. 1:02:46addition to the
  1353. 1:02:48elasticities uh of demand and Supply we
  1354. 1:02:51now are going to care about the
  1355. 1:02:52curvature of demand as well
  1356. 1:02:56um in particular when demand is concave
  1357. 1:02:59when it's negatively curved the
  1358. 1:03:01elasticity of marginal Surplus is going
  1359. 1:03:03to be positive um and that's going to
  1360. 1:03:06tend to make the um uh the pass through
  1361. 1:03:11lower and when the elasticity and when
  1362. 1:03:14the demand curve is convex it's going to
  1363. 1:03:16tend to make the pass through much
  1364. 1:03:18higher um now uh what are some ways that
  1365. 1:03:23we might think about circumstances in
  1366. 1:03:25which the curvature of demand might be
  1367. 1:03:28positive or negative uh Kim do you have
  1368. 1:03:30thoughts about
  1369. 1:03:48that
  1370. 1:03:50okay um well you can think of this as
  1371. 1:03:53how much of the valuation is out in the
  1372. 1:03:55tail
  1373. 1:03:56so if inelastic demand really means
  1374. 1:03:58people have spread out valuations for
  1375. 1:04:00the thing uh curvature is really a
  1376. 1:04:04measure of something like curtosis it's
  1377. 1:04:06like how much is out in the Tails and in
  1378. 1:04:07fact you can relate this to our Notions
  1379. 1:04:09of fat taals before anytime you have fat
  1380. 1:04:12tails and the fatter tails you have the
  1381. 1:04:14more uh negative is going to be one over
  1382. 1:04:18the elasticity of marginal
  1383. 1:04:20Surplus um in fact the elasticity
  1384. 1:04:23marginal Surplus is equal to the
  1385. 1:04:24negative of that parameter Alpha that we
  1386. 1:04:27had before and so 1 over negative Alpha
  1387. 1:04:32is equal to this and so as you get
  1388. 1:04:34towards Zip's law for example this is
  1389. 1:04:36going to get very very uh
  1390. 1:04:40large um so
  1391. 1:04:42income uh tends so when income generates
  1392. 1:04:46values when there's Goods that are
  1393. 1:04:47valued more by the rich than they are by
  1394. 1:04:49others and the more that they're more
  1395. 1:04:50valued by the rich the more that this is
  1396. 1:04:53going to be large or if the if a good
  1397. 1:04:55very Niche appeal then this is going to
  1398. 1:04:58be uh very large so let me give you um a
  1399. 1:05:03graphical illustration of this so here's
  1400. 1:05:06a concave demand function and here's its
  1401. 1:05:10marginal revenue curve which is
  1402. 1:05:12diverging at an increasing rate from the
  1403. 1:05:14demand curve that means that for a small
  1404. 1:05:17increase in marginal cost the increase
  1405. 1:05:20in price is going to be much smaller
  1406. 1:05:21because we move more up the marginal
  1407. 1:05:23revenue curve than we do up the demand
  1408. 1:05:25curve
  1409. 1:05:27on the other hand when we have a
  1410. 1:05:28constant elasticity demand like this
  1411. 1:05:31because these are converging a small
  1412. 1:05:33increase in the marginal cost curve
  1413. 1:05:35leads us to move farther along the
  1414. 1:05:37marginal revenue sorry farther along the
  1415. 1:05:39demand curve than it does along the
  1416. 1:05:41marginal revenue curve and therefore
  1417. 1:05:42leads to twice as large of an increase
  1418. 1:05:44in price as it did um an increase
  1419. 1:05:48in uh uh marginal cost similarly changes
  1420. 1:05:54in the shape of the marginal cost cost
  1421. 1:05:56function which effectively changed the
  1422. 1:05:58elasticity of supply will affect this as
  1423. 1:06:00well so if we have a upward sloping
  1424. 1:06:03marginal cost curve which makes you know
  1425. 1:06:05somewhat inelastic supply then an
  1426. 1:06:08increase in marginal cost leads to a
  1427. 1:06:11smaller move in the quantities and
  1428. 1:06:12therefore a small change in price
  1429. 1:06:14whereas if you have declining marginal
  1430. 1:06:16costs as you often do in natural
  1431. 1:06:18monopolies then an increase that's like
  1432. 1:06:20a negative elasticity of supply then an
  1433. 1:06:22increase in marginal cost leads to a
  1434. 1:06:24bigger change in quantities and
  1435. 1:06:25therefore a bigger change in
  1436. 1:06:28price okay that's it for today

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