ECON20110 Fall 2013 - Lecture 9: Monopoly — Transcript
Full transcript
- 0:01okay so um the basic
- 0:06idea uh of the monopo model is that
- 0:09firms want to try to reduce their
- 0:12quantity in order to raise the price
- 0:14that they receive for their goods in the
- 0:16industry and the reason is that um in
- 0:19order to sell more units a firm needs to
- 0:23lower its price but not just on that
- 0:25last unit but on all of the units that
- 0:28the firm sells
- 0:30and this of course wouldn't arise if
- 0:32firms could charge different prices to
- 0:34each purchase and each purchaser which
- 0:36is something we'll talk about uh just
- 0:39after the
- 0:40midterm um okay so the Monopoly um will
- 0:46tend to reduce quantity below the point
- 0:48where price is equal to marginal
- 0:50cost and that basic effect is something
- 0:54that shows up all over uh the world so
- 0:58um Adam could you give me some examples
- 1:00of cases where firms with Market power
- 1:02reduce their quantities below what you
- 1:04would might think is an efficient
- 1:08level maybe something like uh you VI
- 1:11like a like a organization like a union
- 1:14or something is like a kind of like a
- 1:16monopoly of the labor yeah so like they
- 1:19might have like um they may try to like
- 1:23compat others entering into the the
- 1:26Labor Field or have some like license
- 1:28for the that's a very good example
- 1:31occupational lure uh we didn't talk
- 1:33about that in the first class we did in
- 1:35the previous years uh labor unions who
- 1:38try to stop immigration or have closed
- 1:40shops that stop people from competing um
- 1:43Farm cooperatives try to prevent
- 1:45overproduction of farm products uh drug
- 1:48cartel's main job is not to produce
- 1:51drugs but to stop other people from
- 1:52producing drugs uh and this is the
- 1:55reason that when the drug bar in Pablo
- 1:57Escobar was killed the price of cocaine
- 1:59fell precipitously rather than Rising um
- 2:04uh drug companies make massive
- 2:06investments in trying to reduce the
- 2:10supply of the goods that um they sell by
- 2:15stopping re-importation from poor
- 2:17countries of their products uh strictly
- 2:19delineated territories Etc digital
- 2:22materials of All Sorts are basically
- 2:25free to copy but not free to copy
- 2:28because the law tries to stop you from
- 2:30doing that and companies invest a huge
- 2:31amount in trying to reduce the quantity
- 2:34uh that's supplied movie theaters it
- 2:36basically cost nothing if a movie isn't
- 2:39sold out for an additional person to
- 2:41come and yet they keep people out by
- 2:43charging a price uh which is also
- 2:46obviously
- 2:46inefficient okay so to
- 2:49represent uh this let's say that the
- 2:53revenue that a monopolist earns R of Q
- 2:56is equal to their price which depends on
- 2:58quantity times quantity now under
- 3:00perfect competition they would set price
- 3:01equal to marginal cost and now they're
- 3:03going to set marginal revenue equal to
- 3:05marginal cost marginal revenue is just
- 3:06the derivative of the revenue and uh
- 3:10where's
- 3:11Joan ah there she is hi by the product
- 3:14rule what is the derivative of Revenue
- 3:17what's the marginal revenue equal to
- 3:21um plus der
- 3:26PQ so
- 3:28PQ p Q um so what's the derivative of P
- 3:33of Q * Q yeah P Q Plus p q with Q time Q
- 3:41yeah so oh yeah P of Q yes P of Q um
- 3:46plus P Prime * Q that's right
- 3:49absolutely um so there are two terms
- 3:53here but you're going to set this equal
- 3:54to marginal cost now if this first term
- 3:56was the only thing here then you would
- 3:57set price equal to marginal cost that
- 3:58would be good right this is what happens
- 4:02this is the term that comes from how
- 4:03much benefit the firm gets from changing
- 4:05its quantity holding the price fixed
- 4:06taking itself as a price taker but
- 4:09there's a second term that comes from
- 4:10the impact it has on price experienced
- 4:13on all of its infam marginal units
- 4:15that's the second term which is called
- 4:17Market power or the Coro Distortion or
- 4:19sometimes um the marginal surplus of
- 4:23consumers because what this term is is
- 4:26how much when the quantity increases
- 4:28consumers benefit
- 4:30which uh The Firm doesn't get right so
- 4:33the price is the marginal value that um
- 4:38consumers place on getting the product
- 4:40but not all of that goes into Revenue
- 4:42some of that goes into consumer surplus
- 4:44and that's exactly what this term is
- 4:48here
- 4:50okay
- 4:52um so this term is proportional to how
- 4:55many infam marginal units The Firm has
- 4:57and how much impacts price and those are
- 5:00both measures of how large the firm is
- 5:01if the firm is very small it will have
- 5:03little impact on price and will have few
- 5:05units on which to uh have that impact
- 5:09okay so let's derive some simple
- 5:12examples of this for the most common
- 5:14demand curves let's first start with a
- 5:16concave demand
- 5:17curve
- 5:19um and uh philli could you derive the
- 5:23marginal revenue curve corresponding to
- 5:25this demand curve uh should I go up to
- 5:28the board sure that's probably easiest
- 5:30for people to follow all
- 5:40right
- 5:43oh
- 5:45okay I can yeah
- 5:49please okay so Mr the piece of Q
- 5:54equals P of Q equals um
- 6:001 -
- 6:02q^2 right yeah and
- 6:06then uh Revenue
- 6:09= QP
- 6:12= uh Q 1 - Q 2 = Q - QB exactly and so m
- 6:22r is just a derivative which is Q - 3 q^
- 6:252 1 - 3 q^2 right yeah exactly well done
- 6:31philli thank you
- 6:35um
- 6:36okay so um let me show you what that
- 6:42looks like so here's the concave demand
- 6:46function and you see that as the
- 6:48quantity increases initially marginal
- 6:51revenue and uh and price are at the same
- 6:57point but then they diverge increas inly
- 7:00rapidly as the quantity
- 7:02increases
- 7:04okay um Andrew Adair is not
- 7:09here
- 7:12um Can someone else derive this for
- 7:15linear
- 7:16demand uh so yeah sure so first you find
- 7:20Revenue which is 1 - Q * Q so that's Q -
- 7:24q^2 take the Der of that you get 1 - 2 Q
- 7:28exactly so so this is steeper than
- 7:31demand is so here's linear demand this
- 7:34is steeper than demand is but it
- 7:36diverges at a constant rate right
- 7:39whereas this diverges from demand at an
- 7:41increasing
- 7:43rate okay how about um exponential
- 7:47demand uh Rishi can you derive sure uh
- 7:51yeah sure
- 8:09I'm just going right up
- 8:10here C
- 8:13is uh
- 8:20pus
- 8:25yeah so you got uh
- 8:37Q mhm can I erase this part is
- 8:43yeah I don't think we have an eraser
- 8:45again oh there there it
- 8:51is right so if you derive this you get
- 8:551us the bar of this so you get 2 * 1 2
- 9:03yeah plus
- 9:07uh no he's got a minus around the whole
- 9:09time
- 9:11yeah * 1
- 9:15yeah so you get 1 - 1 + log Q which is =
- 9:22to log Q
- 9:26exactly uh actually negative log q but
- 9:29oh
- 9:30yeah but no that's
- 9:32right okay so this one notice that
- 9:36that's like log q and it was 1 minus log
- 9:39Q so this is just by a constant below uh
- 9:44price right so that is shown in this
- 9:48graph here you see there's always a
- 9:49constant distance between marginal
- 9:51revenue and price so here they were
- 9:53diverging at an increasing rate here
- 9:55they're diverging at a constant rate
- 9:57here there's a constant distance between
- 9:59them so guess what's going to be
- 10:01happening with the last case that I give
- 10:03you uh reishi I'm going to call on you
- 10:06again uh do it for the constant
- 10:08elasticity all
- 10:12right
- 10:21not cool so I'm just going toise one
- 10:33so we have one
- 10:35over 12 right
- 10:39yeah which
- 10:42is yeah so
- 10:47sorry so you take
- 10:51q q * Q you get Q * Q * 1
- 11:0112 yeah and uh if you derive this you
- 11:04get
- 11:0712 12 Q to the 12 which is equal to 1
- 11:13over 2K
- 11:15Q exactly so notice that this is
- 11:21half of the price
- 11:26right and it's decreasing in p uh
- 11:30quantity so that means that these things
- 11:32are going to converge together over time
- 11:34right because there's a constant ratio
- 11:36between them rather than there being a
- 11:38constant difference between
- 11:41them so that's shown here you see
- 11:44they're further apart up here because
- 11:46the ratio between the two of them is
- 11:48always
- 11:49constant okay now how do we find Optimal
- 11:53quantities well imagine that the
- 11:55marginal cost were the x-axis here just
- 11:58for fun
- 11:59then you intersect that with the
- 12:01marginal revenue curve you draw a line
- 12:03up to the demand curve and left over to
- 12:05price in order to get uh the optimal
- 12:08price for the firm to
- 12:09charge okay now another way to write
- 12:13marginal revenue is as price time
- 12:16quantity sorry price of quantity uh Time
- 12:191 minus 1 over the elasticity of
- 12:22demand and uh reishi I'm going to have
- 12:25you dve that again as well
- 12:34I swear it's
- 12:44[Music]
- 12:54random 1 - one Epsilon is that yeah okay
- 13:04um so no it's not P of Q equals that
- 13:06it's marginal I want to claim that
- 13:08marginal revenue is equal to P of Q * 1
- 13:12- 1 Epsilon the question is how could
- 13:14you prove that that's the
- 13:20case um times P of Q
- 13:26oh so we have a we had a form for
- 13:29marginal revenue before can you
- 13:30transform it into that um okay so we had
- 13:35from before that marginal revenue
- 13:39equals P Q Plus it's p Prime of Q * Q
- 13:46sorry I pime of Q * Q Plus p q yeah
- 13:52okay
- 13:56um so
- 13:59if
- 14:03you well here you've got your P of Q
- 14:06term right which shows up there so this
- 14:08much must correspond to this term
- 14:10somehow right okay so I mean if you got
- 14:14your cuz you don't have a p of Q um
- 14:18unless
- 14:20you so why don't you try factoring a p
- 14:23of Q out of the whole expression P of Q
- 14:26yeah okay
- 14:29then you get 1
- 14:33plus
- 14:37um yeah
- 14:391 p
- 14:44q q q over
- 14:47PQ okay now oh okay does that look like
- 14:51an elasticity yes it is so right which
- 14:56you which is equal to yeah yeah two
- 15:01* 1
- 15:05plus right except that the elasticity of
- 15:08demand is negative so yeah exactly just
- 15:12to be a little bit more explicit this is
- 15:14DP DQ which is 1 over uh DQ
- 15:19DP right and then it's divided by you
- 15:22know q and multiplied by P and that's
- 15:25exactly the elasticity
- 15:27formula what did you say
- 15:29no you're done you're done my
- 15:33friend um okay so one thing that
- 15:36immediately tells us is that marginal
- 15:37revenue is negative whenever the
- 15:39elasticity of demand is less than one
- 15:42which means that the monopolist will
- 15:44never produce in a region where demand
- 15:46is in elastic because he'd always have
- 15:48an incentive to reduce his
- 15:50quantity um which would also reduces
- 15:53cost so the elasticity of demand can be
- 15:57seen as one thing one way of formalizing
- 16:00the notion of Monopoly power if the
- 16:02elasticity is small then the relative
- 16:05importance of that firm is small um if
- 16:09the elasticity is large that firm is
- 16:12relatively important to the market and
- 16:14it summarizes the notion of being sort
- 16:16of a big player and rearranging this
- 16:18setting uh this equal to marginal cost
- 16:21yield that the price minus marginal cost
- 16:24divided by Price that's called the
- 16:25relative markup is equal to the inverse
- 16:27elasticity of demand so the smaller the
- 16:30elasticity is the larger the markup The
- 16:32Firm charge is which is a natural
- 16:33measure of Monopoly
- 16:36power okay now of course there's other
- 16:39measures of Market power you could also
- 16:41create it's not obvious this is the best
- 16:43one another one you could create is the
- 16:45markup divided by the marginal cost
- 16:47rather than divided by the price and
- 16:49that's equal to 1 over the elasticity
- 16:51minus one or you could do the price to
- 16:53marginal cost ratio which is equal to
- 16:54the elasticity over the elasticity minus
- 16:56one or you could do the absolute markup
- 16:59which is equal to the price divided by
- 17:00the elasticity these are all very
- 17:02similar ways of measuring Market power
- 17:05um and some are more useful than others
- 17:07depending on the context so the standard
- 17:10learner formula is useful because it's
- 17:12so simple and it uses elasticity so
- 17:15directly the price cost ratio is
- 17:18useful uh for profits um especially when
- 17:23you have a constant marginal cost um
- 17:26because it yields just like the ratio
- 17:30between whatever the cost is and however
- 17:32much uh profits the firm is making um
- 17:37the uh markup to cost gives a measure of
- 17:41profitability the absolute markup is
- 17:44useful when costs are not positive which
- 17:46can happen for example in credit cards
- 17:49you know your credit card subsidizes you
- 17:52for using your card you get points for
- 17:54using your card because they're earning
- 17:56money off of interchange fees from
- 18:00Merchants that pay them when they use
- 18:01the card and so denominating things by
- 18:04cost can be problematic then
- 18:08um okay now of course to set these
- 18:12prices firms need to know what the
- 18:13demand curve is otherwise the quantity
- 18:16that they produce will not match uh
- 18:18demand and um to so as a result firms
- 18:23need to be able to draw out their
- 18:25marginal revenue curve and it used to be
- 18:28that firms just had to guess about this
- 18:30and gradually learn but the internet has
- 18:32really created a revolution in this
- 18:34extent because many companies are
- 18:36experimenting with prices all the time
- 18:38to try to figure out what demand is this
- 18:40is particularly common on eBay where
- 18:43sellers all the time are experimenting
- 18:45with the reserve price that they can
- 18:46charge on their
- 18:48auctions you know sometimes the same
- 18:50seller will sell the same good on a
- 18:52different day or even at the same time
- 18:55uh at different prices or different
- 18:57Reserve prices uh in order to tryy to
- 18:59see what demand is like now this is an
- 19:03auction yeah Christian sorry what's the
- 19:05reserve price uh a reserve price um is
- 19:11the lowest price that you'll accept
- 19:13without calling the auction off oh so
- 19:16it's like a starting price
- 19:18basically um now changing the reserve
- 19:22price uh is a lot like changing a price
- 19:25and it traces out something like a
- 19:26demand curve why why is that true what
- 19:29sort of demand curve could you create uh
- 19:32Evan using uh Reserve changing around
- 19:35the reserve price to affect uh prices
- 19:38and and the probability of sale so you
- 19:40want so you want me to explain why it
- 19:42would look like a demand or or what yeah
- 19:45how you know this is a starting price
- 19:47for an auction it's not like a price
- 19:49that I charge you know and the number of
- 19:52sales I get but you can get out of this
- 19:54something that's like a demand curve
- 19:55well instead of the number of sales you
- 19:58you could could look at for example the
- 20:00number of people who are going to be
- 20:01willing to bid or you could look at what
- 20:05kind of price of how much you can expect
- 20:07it to go up right or if it's going to or
- 20:10the or the probability of it um that's
- 20:13going to actually clear yeah so I think
- 20:16the easiest thing to correspond to is
- 20:18the probability that it actually clears
- 20:20right because if you set a higher
- 20:21reserve price the chance that it clears
- 20:23is going to be lower but what's the
- 20:25offsetting benefit you get when you set
- 20:26a higher reserve price you get more
- 20:28money why the reason why you get well I
- 20:32suppose it's that you're more likely to
- 20:35get to get more money right and the
- 20:36reason why is because let's suppose that
- 20:39you have one auction where you have the
- 20:41same item with a lower reserve price and
- 20:44you have for whatever reason one person
- 20:47who bids that Reser that lower reserve
- 20:49price in the first auction that's what
- 20:51you're going to get the second option if
- 20:53that person is still willing to pay
- 20:55higher then you then you get that money
- 20:57you can't get the lower exactly right so
- 20:59basically there are two circumstances
- 21:01where the reserve price matters one is
- 21:03one one in which if you'd set a lower
- 21:05reserve price someone would have bid
- 21:07above it but because you said a higher
- 21:09reserve price no one bids above it
- 21:12that's the case in which the reserve
- 21:13price deterred a sale from taking place
- 21:16on the other hand if you there's another
- 21:19circumstance which is that the um the
- 21:23low the second highest bid if there was
- 21:26one was below the reserve price that you
- 21:29set but um the highest bid was above it
- 21:32in that case it raises the price that
- 21:34you get um and so you can look at the
- 21:39average price that you get for a good as
- 21:41a function of your reserve price graphed
- 21:44against the um the probability of sale
- 21:48and those things will have a negative
- 21:49relationship the higher reserve price
- 21:50you set the higher average price you'll
- 21:52sell it at but also the lower will be
- 21:54the probability of sale and that'll
- 21:56Trace out something like a demand curve
- 21:57Yeah Austin this is not I guess strictly
- 22:00the same thing but I know on eBay
- 22:02typically they'll tell you whether the
- 22:03reserve price was met or not or not
- 22:05whereas like an art auctions and things
- 22:06it's typically private that don't tell
- 22:08you with the reserve do you get any like
- 22:10discontinuities related to that people
- 22:13you know just trying to barely clear it
- 22:14or
- 22:15something so people always barely I mean
- 22:18it's always people's incentive to First
- 22:20barely clear it uh in in the art
- 22:22auctions that incentive doesn't exist
- 22:24and a reserve price doesn't actually
- 22:25raise your Revenue all it does is stop
- 22:27the thing from being sold at a
- 22:29inefficiently low
- 22:31price
- 22:36um so yeah okay so uh luron inov uh
- 22:43Teresa coer John Levan uh and Neil
- 22:48sueras got all of eBay's
- 22:51data and they found 500,000 cases in
- 22:56which people had run experiment
- 22:59so you you guys probably know John list
- 23:02here runs lots of experiments
- 23:04right but um what they found was that um
- 23:11you don't just need to be an economist
- 23:13who goes out and runs experiments
- 23:15yourself sellers on eBay are running
- 23:18experiments all the time and so rather
- 23:20than running you know I don't know five
- 23:21or 10 experiments you could look at
- 23:23500,000 experiments by looking at what
- 23:26the sellers are choosing to do
- 23:27themselves
- 23:28and so um what they did is they looked
- 23:32at cases where the same seller sold the
- 23:34same item on slightly different terms
- 23:38either at the same time or at slightly
- 23:39different times and they use this to
- 23:41draw out demand curves for the auction
- 23:44just as I was describing and the
- 23:47interesting thing is they found that all
- 23:48these demand curves at a very similar
- 23:50shape yeah Evan so on eBay is there a
- 23:53penalty for listing the same item
- 23:54multiple times and then canceling the
- 23:56$999 they get the lowest price before
- 23:58they close oh I think there is yeah so
- 24:02you you have to agree to sell so then
- 24:04what so then what are they doing are
- 24:05these sellers who who have an inventory
- 24:08and then list the inventory I think
- 24:09that's the point they're trying to
- 24:10figure out what the market price should
- 24:12be by trying out different prices and
- 24:14then for the future yeah
- 24:17okay um so the interesting thing that
- 24:20they found is that marginal revenue is
- 24:22actually increasing in some parts
- 24:25um and so
- 24:29uh the cost if you think about it in
- 24:32this case is the value you could get by
- 24:35trying to sell that object again or
- 24:36keeping it yourself right and there's a
- 24:39possibility of there being multiple
- 24:40intersections between marginal cost
- 24:42which is constant as a function of the
- 24:44probability right it's just the value of
- 24:46that good and the average and the uh
- 24:50marginal
- 24:51revenue okay so let me show you a
- 24:53picture of this and show you what we do
- 24:55to analyze these cases so here's what
- 24:57they found they found that for tons of
- 24:59different Goods if we divided the uh
- 25:03price of the Good by the um assessed
- 25:08value that um the demand curves looked
- 25:13very similar to one another and they
- 25:15looked like this they were sort of
- 25:18reasonably sloped here but then they get
- 25:20incredibly flat as you get out to high
- 25:22probabilities why is that well as a
- 25:26object is getting down to a low low
- 25:28probability of sorry a low price there's
- 25:31always going to be someone on eBay who's
- 25:33just looking for deals who's going to
- 25:36snap that thing up and go resell it
- 25:38right and so that makes demand really
- 25:41have a very sharp floor underneath it
- 25:45these people up here are people who are
- 25:46actually going to keep that good these
- 25:48people down here are people are just
- 25:49going to go and resell it again right um
- 25:54and uh you can fit a curve through this
- 25:58you can just you know use a polinomial
- 26:00fit on Excel and you can fit a third
- 26:02degree polinomial through this and you
- 26:04get a marginal revenue curve that is not
- 26:07just decreasing like all those marginal
- 26:09revenue curves we looked at before which
- 26:11means that if you had a marginal cost
- 26:13that was right here there would be three
- 26:15intersections between marginal cost uh
- 26:18and
- 26:19demand now does anyone want to guess
- 26:22imagine that marginal cost were here
- 26:26which point of these three would
- 26:28actually be the optimal quantity for you
- 26:30to
- 26:31sell the optimal probability with which
- 26:34a sale would
- 26:39occur marinal cost this way again sorry
- 26:42marginal cost let's say it's at 75 so
- 26:47it's just below that black line
- 26:54I what do you think so is the area like
- 26:56of those two little regions like the
- 27:00yeah between the pink and the black line
- 27:01are those equal yes that's the point but
- 27:04you have to figure out why that's the
- 27:05case that's what I'm trying to take you
- 27:07guys through
- 27:15now well notice that the profits that a
- 27:18firm earns is the area between the
- 27:20marginal revenue curve and the um
- 27:24marginal cost curve up to the point that
- 27:27they go to so if the firm produces here
- 27:30they get all this area and profits but
- 27:32they don't get anything over here if
- 27:34they produce over here they're going to
- 27:36actually take losses in this region down
- 27:38here and then they'll make gains over
- 27:41here but the gains are bigger than the
- 27:43losses here right the area above is
- 27:45bigger than the area below and so
- 27:47they'll produce over here on the other
- 27:50hand if they had a cost that was 85 like
- 27:53up here then if they produced over here
- 27:56they'd take losses over this full region
- 27:58here and only make gains over here which
- 28:00would not be worth it so they'd be
- 28:02better off producing over here so this
- 28:05line which is called the ironing line is
- 28:07a line where area above the line and
- 28:09below the curve equals the area below
- 28:11the line and above the curve and that is
- 28:15exactly the cost at which they would
- 28:18jump from producing from selling with
- 28:21this probability to selling with this
- 28:23probability so if the co if someone's
- 28:26cost went from you know know 79 to 82
- 28:31you would see the price jump from on
- 28:34average from about what is this
- 28:3882 up
- 28:40to uh
- 28:431.05 right so there would be a
- 28:45discontinuous change in price when there
- 28:47was a continuous change in the cost and
- 28:50the reason is that you're basically
- 28:53making a decision of which of two
- 28:54markets to serve are you going to try to
- 28:57just give this to the resellers and let
- 28:59them resell it in which case you'll set
- 29:00basically a zero reserve price or are
- 29:03you going to try to really sell this to
- 29:07a final consumer only in which case
- 29:09you'll probably set a reserve price
- 29:10that's about equal to its value does
- 29:12that make
- 29:14sense so this technique ironing is a
- 29:17more General technique you can use
- 29:18anytime you have a
- 29:20non-monotonic uh marginal revenue curve
- 29:22or really non-monotonic anything
- 29:24function that you have to optimize in
- 29:25economics you can always replace it with
- 29:27a mon iic one by using ironing
- 29:30procedures like this canceling out the
- 29:32area above and below
- 29:35yeah the IR line was determined by like
- 29:39who wants to resell wants to keep it
- 29:41finally you just talk a little more
- 29:43about well so I mean this is just a
- 29:45hypothesis but the reason these demand
- 29:47curves look they have this shape where
- 29:49they're like quite steeply decreasing
- 29:52and then you get out to about a0 five
- 29:54probability of sale and they're almost
- 29:56totally flat after that and the reason I
- 29:58think is that basically the people who
- 30:01are buying it and showing up with about5
- 30:05probability are people who actually want
- 30:06to keep that thing
- 30:08forever and they have like a decreasing
- 30:10demand curve but people who just want to
- 30:12resell it their value is completely
- 30:14constant because they all just have the
- 30:15same cost of reselling it
- 30:20right
- 30:22okay so Monopoly is two basic welfare
- 30:26related effects compared to
- 30:28competition the first is that it
- 30:31transfers resources um to the
- 30:35monopolist
- 30:38um from uh the consumers and the second
- 30:41is it inefficiently reduces the output
- 30:44in the
- 30:45industry so how do we know Mike fosco
- 30:49how do we know that this reduction in
- 30:51quantity is socially inefficient uh from
- 30:53the dead rate loss we're um the they're
- 30:56not producing uh Aral cost is equal to
- 30:59the price they're doing less than that
- 31:02okay so why does that create dead weight
- 31:03loss because there are more gains to be
- 31:06made for society in general if you
- 31:08produce more output um because then the
- 31:10benefit to the consumer is greater than
- 31:12the uh
- 31:15lower Yeah so basically this is a case
- 31:18in which at Price equals marginal cost
- 31:21the value the consumer gets is exactly
- 31:24equal to the cost of the firm of
- 31:26producing if the price is above the
- 31:28marginal cost the consumer gets a
- 31:29greater value out of the product than
- 31:31the than the cost of producing it and
- 31:34therefore it would be socially valuable
- 31:35to produce more of it and the firm is
- 31:38eliminating some sales that would be
- 31:40beneficial because the benefit to the
- 31:43consumers would be greater than the cost
- 31:46okay
- 31:48um now uh the inefficiency of Monopoly I
- 31:53think is quite apparent in real life
- 31:56it's the reason why information Goods
- 31:57like music aren't freely available right
- 32:01it's the reason why there are empty
- 32:02parking lots in busy cities uh that
- 32:07charge High rates right like it's
- 32:09completely crazy for there to be parking
- 32:11lots that are empty and people who are
- 32:13roaming around the streets looking for
- 32:15places to park right because there's no
- 32:17cost of have on the margin of putting
- 32:19one more person into that parking lot
- 32:21and there's a big uh cost of having them
- 32:24roaming around the streets right
- 32:28uh yeah Evan couldn't you see the high
- 32:30parking rates as as just a fee of the
- 32:34people who are going to park in that
- 32:36area are paying to increase the
- 32:38probability there is a
- 32:39spot because I'm from one of those very
- 32:41crowded areas and it's not normally the
- 32:43case people are driving around because
- 32:46there's not a spot in the parking lots
- 32:47because even with high prices it's
- 32:49usually
- 32:49full really I don't think that that's
- 32:52true I don't think it's usually true
- 32:54that parking lots usually have a fair
- 32:56number of vacancies in in almost all
- 32:59times of the day I mean there's a few
- 33:00parking lots that fill up at a few times
- 33:02of the day but it's very rarely the case
- 33:04that all the parking lots are actually
- 33:06full so uh yeah Austin are parking lots
- 33:10really monopolies though I mean I feel
- 33:12like for parking lots at least it's more
- 33:14of the case where it's yeah so that's a
- 33:15good question I don't think that
- 33:17structurally they're monopolies but I
- 33:19think it's basically they are monopolies
- 33:21because once you've turn you can't
- 33:22figure out what the price of the parking
- 33:24lot is until you've already turned into
- 33:26the parking lot and then I mean in other
- 33:28words like people have to invest like
- 33:30resources to learn the prices of the
- 33:32parking lot if there was complete price
- 33:34transparency I think it would
- 33:35effectively be perfect competition and I
- 33:37think that's starting to happen because
- 33:39of this app best parking I don't know if
- 33:41you guys have this I love this app and
- 33:43it like tells you the rates of all the
- 33:44parking lots and I think if everyone
- 33:46comes to have that app then there will
- 33:47be perfect competition but I think that
- 33:49not everybody has it yet and so there is
- 33:51effectively Monopoly are there any
- 33:52dynamically priced parking lots in
- 33:55Chicago well I mean there's almost all
- 33:57almost all parking lots have some amount
- 33:58of dynamic pricing they all have like
- 34:00you know special deals but not really
- 34:03intelligently dynamically priced ones no
- 34:06I mean they're like the way they
- 34:07dynamically price is better than none
- 34:09but it's not as intelligent as you could
- 34:10with a really adaptive system but to
- 34:12really make something like that work
- 34:13You' need price transparency on that as
- 34:15well so you'd need to have like the app
- 34:17linked to the prices and people would
- 34:20have to like have their apps telling
- 34:22them which lot to go to based on its
- 34:24current you know occupancy and your for
- 34:27a price I think I read San Francisco's
- 34:28doing that now yeah I think cities in
- 34:31California are trying that 100 yeah what
- 34:33what what things isn't California doing
- 34:35better than the rest of the world I mean
- 34:38I'm a Californian
- 34:41um um okay so
- 34:45effectively Monopoly means that
- 34:48consumers have an externality on the
- 34:52firm because if they purchase more the
- 34:54firm is going to make more profits
- 34:55because the firm is earning a markup
- 34:57over marginal cost on every unit that it
- 34:59sells and these extra profits that are
- 35:02created are not mediated through the
- 35:03price system so there are real
- 35:05externality and they suggest a standard
- 35:08pigouvian Solutions like subsidizing
- 35:10purchases of the goods by consumers or
- 35:13perhaps regulating the firm's price down
- 35:15to cost or mandating an efficient
- 35:18quantity uh to be produced and we're
- 35:20going to talk about some of these
- 35:22policies in practice on Thursday but
- 35:24they're far less common that you'd think
- 35:27and in lect 13 we're going to talk a
- 35:28little bit about why despite the
- 35:30ubiquity of Market power we don't have
- 35:32solutions that really uh address them
- 35:35that that often now you know another
- 35:38thing to keep in mind is that there are
- 35:40other solutions that you could use to
- 35:42address Market power which maybe are
- 35:45seem a little bit more dirty uh or less
- 35:49clearly cleanly lined up with economics
- 35:51but are you know from a social
- 35:53perspective just as valuable so for
- 35:55example advertising or creating Prestige
- 35:59for products can make people value them
- 36:03more and that can cause consumers to buy
- 36:08at prices that are above what they're
- 36:09willing to pay and therefore offset the
- 36:12Distortion associated with Monopoly so
- 36:14some sort of deceptive advertising or
- 36:17building hyper on a product might
- 36:18actually be socially beneficial because
- 36:20it offsets the Monopoly
- 36:23Distortion we consider that paying more
- 36:25than the what like that's considered
- 36:28paying more than their willing well I
- 36:29mean imagine you like a lot of people
- 36:31say oh they trick you into making you
- 36:32feel like you want the product when you
- 36:34don't really want it or you're willing
- 36:35to pay more than you're really willing
- 36:37to pay but that could actually be good
- 36:38in the context of a monopolized product
- 36:40because otherwise it would be
- 36:40inefficiently
- 36:42underconsumed uh yeah but like in that
- 36:44scenario though um although you'd be
- 36:46producing the right output like the
- 36:47right right quantity like the benefit
- 36:50would be transferred from like conser to
- 36:52the yeah that's true okay so but still
- 36:56from a social perspective
- 36:58in in aggregate it's still value and in
- 37:00fact it might even be good to transfer
- 37:01to the firm if the firm innovated in
- 37:03order to create that product because
- 37:06that gives more incentives for
- 37:07Innovation yeah Evan why is it that the
- 37:09soci social socially optimal quantity
- 37:12hasn't changed in response to the
- 37:14advertising because if now you change
- 37:15how people value it why well I mean it
- 37:17all depends how you think about
- 37:18advertising but some people think about
- 37:20advertising as sort of deceptive and
- 37:22making you feel like you want something
- 37:23more than you really want it and that
- 37:25wouldn't change the socially optimal
- 37:26quantity so you're saying that if you
- 37:28think of it there's like still a
- 37:30constant real want yeah so there there's
- 37:33a paper by Dixit and nor uh and Norman
- 37:37which is all about that uh yeah if we
- 37:40assume that people have a constant real
- 37:43want then uh be being able to
- 37:47deceptively advertise
- 37:50essentially someone allow it allows the
- 37:53monopolist to appropriate some money
- 37:56that
- 37:59is uh that consumers really aren't
- 38:02willing to pay so might it create too
- 38:04much incentive yeah so you'll typically
- 38:07want like you'll spend too much on
- 38:08Advertising but it will also typically
- 38:10be bad if you don't allow advertising at
- 38:15all
- 38:16so okay so the debt the like any tax or
- 38:20externality the value of extra
- 38:23production will be equal to the wedge
- 38:25the sort of like uh uh difference
- 38:28between price and marginal cost times
- 38:30the change in quantity uh that occurs
- 38:32when when something changes yeah ver um
- 38:35so even though that like allocates like
- 38:38a socially optimal level uh does it
- 38:40still create like negative externality
- 38:43because um consumers buy more than like
- 38:45they so advertising will have a negative
- 38:47externality because you'll be taking
- 38:49money from consumers and giving it to
- 38:50the firm and it's an action taken by the
- 38:52firm so it does have a negative
- 38:54externality but on the other hand it
- 38:56might be more efficient then completely
- 38:58Banning that activity so you might want
- 38:59to tax advertising but you wouldn't want
- 39:01to eliminate it
- 39:03entirely um yeah Christian so would that
- 39:05be a real externality of advertising
- 39:08yeah can you it's real because it affect
- 39:13it hurts the consumers but doesn't
- 39:15benefit anyone other than the firm and
- 39:17so the firm's the one
- 39:22doing okay um so as a result we can
- 39:27measure
- 39:28the dead weight loss using the standard
- 39:30dead weight loss triangle the only
- 39:32difference is now the size of this
- 39:34triangle is determined by the Monopoly
- 39:36Optimum and in particular it has a
- 39:38particular relationship to Monopoly
- 39:40profits that we'll explore in a minute
- 39:42and this is the triangle bounded by the
- 39:44supply curve the demand curve and the
- 39:45equilibrium quantity now we can measure
- 39:48Monopoly profits graphically in two ways
- 39:51one is the area between the equilibrium
- 39:53price and marginal cost or the area
- 39:56between marginal revenue and marginal
- 39:58cost so let me show you that so the area
- 40:02between price so if this is the marginal
- 40:05cost curve and this is the marginal
- 40:08revenue curve here is the price and
- 40:12profits are either the area between this
- 40:14price and marginal cost C plus d or the
- 40:17area between uh marginal revenue and
- 40:20marginal cost which is a plus c and you
- 40:23notice by similar triangles these are
- 40:24the same areas wait which which what
- 40:27what what each l so this is the demand
- 40:30this is the marginal revenue this is the
- 40:32marginal cost so this is the optimal
- 40:35quantity and the optimal price so here's
- 40:38profit the area between price and
- 40:40marginal cost or profit the area between
- 40:43marginal revenue and marginal cost and
- 40:45they're the same by similar
- 40:48triangles we can also measure consumer
- 40:50surplus is either the demand between the
- 40:53area between demand and price that's the
- 40:55way we usually measure it that's a plus
- 40:57be up here right but you can also
- 41:00measure it as the area between demand
- 41:02and the marginal revenue curve because
- 41:04remember that the difference between de
- 41:06uh demanded marginal revenue is the uh
- 41:08marginal surplus of those consumers so
- 41:11it's the area B plus d which Again by
- 41:13similar triangles is the same as the
- 41:15area a plus
- 41:17b
- 41:19okay
- 41:22um so
- 41:26um the dead weight loss
- 41:29triangle is
- 41:31e the area over here because this would
- 41:35have been the efficient quantity and
- 41:37here's all the loss in willingness to
- 41:39pay minus marginal cost that occurs
- 41:41between
- 41:42those
- 41:44okay now um Alfred Marshall who is uh
- 41:48not only one of the you know most famous
- 41:51economists of all time but also was um
- 41:57sort of the founder of price Theory
- 41:59which is the school of Economics that
- 42:01The Chicago School uh is so into um said
- 42:06that you can think about almost
- 42:08everything in economics in terms of tax
- 42:11incidents and you probably learned in
- 42:13both your basic courses and probably
- 42:14last term the basic principles of tax
- 42:17incidence for uh perfect competition and
- 42:20use those to think about all sorts of
- 42:22different types of interventions uh that
- 42:25happened in markets
- 42:28now most of what's different under
- 42:30Monopoly remember that Monopoly models
- 42:32are really only useful for thinking
- 42:33about interventions that occur directly
- 42:35through the actions of that firm and so
- 42:38if we just think about the incidence of
- 42:40changes to that firm we can think about
- 42:42most interventions that are relevant to
- 42:44Monopoly so I want to give a brief recap
- 42:47of compet perfectly competitive
- 42:48incidents and then I want to contrast
- 42:50that to
- 42:51monopo and um Evan could you tell us
- 42:55some of the principles of incidence
- 42:57under perfect
- 42:59competition um
- 43:03princip incidence of
- 43:15taxes can't remember
- 43:17it um anybody else want to yeah Phil um
- 43:22in the short run uh because
- 43:28well in the long run the incidence is
- 43:30purely on consumers because a firms need
- 43:35to enter and exit to maintain zero
- 43:38profits in equilibrium well if in the
- 43:40long run the demand the supply curve is
- 43:42extremely elastic and the demand curve
- 43:44is not so elastic but yeah um yeah
- 43:48assuming assuming infinite using that a
- 43:52standard
- 43:53elasticity yeah but I mean even more
- 43:56basic than than that
- 43:58uh tavish whoever has the more
- 44:02elastic
- 44:05supp yeah that's the most that's one of
- 44:07the most basic principles so the most
- 44:09basic principle is that the physical
- 44:11incidents who literally pays the tax is
- 44:14irrelevant to who actually Bears the
- 44:17burden of the tax because if we charge
- 44:20tax on the consumers the price of the
- 44:22good will fall if we charge tax on the
- 44:25producers the price of the good will R
- 44:27in response to that most likely right
- 44:30and um therefore we can always treat the
- 44:33tax as if it's directly paid by the
- 44:35producers and then just study how it
- 44:37gets passed through to Consumers and I'm
- 44:40going to call that rate of pass through
- 44:41the rate at which the price increases
- 44:42when the tax increases uh
- 44:45dpdt uh the pass through rate
- 44:48row so then the fraction of the tax that
- 44:54ends up getting paid by the
- 44:55consumers uh is going to be equal to the
- 44:58pass through rate and the fraction
- 44:59that's paid by the producers is 1 minus
- 45:01the pass through rate right and all of
- 45:05the tax is borne by one side or the
- 45:07other right if we have put in a small
- 45:10tax all of that tax is born either by
- 45:13the consumers or the producers so if we
- 45:16want to call the incidence the ratio of
- 45:18the amount borne by the consumers to the
- 45:20amount born by the producers that will
- 45:22be row over 1 minus
- 45:24row okay so the second principle and
- 45:27this is what tavish was getting at is
- 45:30that the inelastic side of the market
- 45:32Bears the um tax uh in particular the
- 45:36pass through rate is equal to 1 over 1
- 45:38plus the elasticity of demand over the
- 45:40elasticity of supply and Tanner could
- 45:44you derive that
- 45:46formula you'll probably want to do it on
- 45:48the board yeah sure
- 46:09can I ER yeah please uh there's there's
- 46:11a eraser if you want it where's
- 46:23that so I'm driving the uh the price one
- 46:26over 1 plus the man Supply right yeah
- 46:34okay it's the pass through is equal to
- 46:36one oh pass yeah yeah sorry so to derive
- 46:39the pass through rate remember you need
- 46:41to do a comparative static it's how does
- 46:43the price change when the tax changes
- 46:45right so what's the equilibrium
- 46:47conditions in the market
- 46:50um just it's demand equals Supply right
- 46:54but remember that the producer doesn't
- 46:56get the full price he only gets the
- 46:57price minus the tax so how would you set
- 46:59up the equilibrium conditions for
- 47:02that let's see
- 47:20so we want to find the change in price
- 47:23as the as the tax the change change in
- 47:25price of the tax happens yeah so what's
- 47:27the first just write down the
- 47:29equilibrium condition so demand is a
- 47:32function of
- 47:41price just D of P right that's just a
- 47:43function D of P or D of P like demand of
- 47:49price is equal to the supply is a
- 47:51function of price minus the tax right
- 47:56right yeah okay so now how would you
- 47:59figure out how the price changes with
- 48:01respect to the
- 48:02tax uh take size
- 48:13yeah so by the implicit function theorem
- 48:15you have to put dpdt here and you have
- 48:18to put dpdt minus1 there
- 48:28yeah you heard parentheses I know okay
- 48:32so now you need to solve for dpdt which
- 48:33is the pass through r
- 49:22good
- 49:29you can drop the arguments inside of
- 49:30those things it'll make your life
- 49:37easier right okay and then try dividing
- 49:41through both the top and the Bottom by S
- 49:45Prime by S Prime
- 49:54yeah no don't don't divide both sides
- 49:58just divide the top and the bottom of
- 49:59this expression
- 50:07by yeah D Prime over S
- 50:11Prime yeah you go to a negative there
- 50:14this but and put a negative in Fr of
- 50:17this
- 50:18yeah
- 50:20um yeah and then note that D Prime over
- 50:25S Prime is equal to the e of demand over
- 50:27the elasticity of supply because both
- 50:29have the same price and the same
- 50:31quantity right at equilibrium and so
- 50:35that's how you get this
- 50:37formula heroic job Tanner thank you um
- 50:41okay so just to give you an intuitive
- 50:43sense for this suppose that um the
- 50:47demand curve is totally inelastic and
- 50:49the supply curve is somewhat elastic
- 50:51then look the consumers are going to
- 50:53Bear all of the tax if we put the tax on
- 50:56the price price Rises exactly by the
- 50:57amount of the tax and the consumers bear
- 51:00it
- 51:01all um on the other hand if the supply
- 51:05is perfectly elastic and then when the
- 51:09um demand is perfectly elastic then when
- 51:12the supply uh when the tax Rises the um
- 51:17price is going
- 51:19to
- 51:21uh then the price is going to stay the
- 51:24same and the amount received by the the
- 51:26firm is going to fall by exactly the
- 51:28amount of the tax and therefore the firm
- 51:30will bear all the incidents right now
- 51:33more generally if both are elastic it
- 51:36depends on the relative elasticity of
- 51:38the two curves um as shown here
- 51:43okay now if we keep raising the tax on a
- 51:46market if we start with a small amount
- 51:49and we raise it f higher and higher at
- 51:51some point we're going to reach a tax
- 51:53that's so high that no one's willing to
- 51:55buy the product at all anymore more
- 51:57right and we can work backwards from
- 51:59that point to determine the total amount
- 52:01of consumer surplus right so because
- 52:04once we reach a tax of T there's no
- 52:06consumer surplus the consumer surplus is
- 52:09just going to be the integral of the
- 52:11pass through rate times the quantity
- 52:13because that's how much the consumers
- 52:15lose every time we raise the price by a
- 52:17little by the tax by a little bit and
- 52:20the producer Surplus is going to be the
- 52:22integral of one minus the pass through
- 52:24rate times the quantity so if we then
- 52:26let the average pass through rate be the
- 52:28quantity weighted average of pass
- 52:30through between a tax of zero and the
- 52:34maximum tax then the global incidence
- 52:38the ratio of total consumer to Total
- 52:40producer Surplus is the ratio of the
- 52:42average pass through over one minus the
- 52:44average pass through right so you know
- 52:49often when you say the consumer Bears
- 52:51the weight of a tax you want to think oh
- 52:55poor consumer he has to pay all the tax
- 52:58but in reality the only reason the
- 52:59consumer is bearing the weight of the
- 53:00tax is that the consumer is the one who
- 53:02benefits from the market existing in the
- 53:04first place right the person who Bears
- 53:07the tax is the person who benefits from
- 53:08the market being there right um so the
- 53:14global ratio of consumer to producer
- 53:16Surplus is just the uh quantity weighted
- 53:21average of the ratio that happens for a
- 53:24small change in the tax rate
- 53:28so the inelastic side is the one that
- 53:30benefits from the market existing
- 53:32they're the ones who really need it to
- 53:33be there whereas the elastic side
- 53:35doesn't care whether the Market's there
- 53:37or not they're H just as happy either
- 53:38way
- 53:43okay now um under Monopoly there's going
- 53:47to be a fundamentally uh there incidence
- 53:51is going to be fundamentally different
- 53:52in a couple of ways so it's still going
- 53:55to be the case that physical and
- 53:58economic incidents are independent of
- 54:00one another um because it doesn't matter
- 54:03whether you tax the consumer or the
- 54:05producer but now rather than the tax
- 54:07being split between the two sides
- 54:10there's actually going to be an excess
- 54:12burden because too little of the good is
- 54:14already being produced there's going to
- 54:17be more loss to the firm and the
- 54:20consumer than is uh the revenue that the
- 54:23government
- 54:24gets um
- 54:27in particular The Firm chooses its
- 54:30quantity so as to maximize prices and
- 54:33its profits are given by this formula so
- 54:36what is going to be the loss to the firm
- 54:38when the taxes increase by a little bit
- 54:41uh reishi and you can use the envelope
- 54:43theorem uh see if you can use the no no
- 54:46don't look uh see if you can use the
- 54:48envelope theorem to figure out really
- 54:51simply uh what the effect of a change in
- 54:53the tax is on the firm's profits in this
- 54:57okay
- 55:03um remember the quantity is being chosen
- 55:06optimally right
- 55:11right the tax changes by a very small
- 55:15amount
- 55:18the quantity
- 55:21also the quty also Chang
- 55:23by that's true but it's not enough what
- 55:28does the envelope theorem tell us to
- 55:30do to differentiate with respect respect
- 55:37Quan yeah it says that we can hold fixed
- 55:41anything that's being
- 55:42optimized right when we take the
- 55:44derivative of the thing that it's
- 55:46optimizing right so here what that what
- 55:48would that tell us the effect of the tax
- 55:50on profits is um you can hold profits
- 55:55you can hold quantity
- 55:56that's the thing you're choosing to
- 55:59optim
- 56:01so would it just
- 56:05be quantity F would just be the um the
- 56:10Der with respect
- 56:15to T directly right so just be um
- 56:21negative uh just Q minus just negative
- 56:26Q yeah so the monopolist because he
- 56:29chooses his quantity to maximize profits
- 56:33um Bears the full burden of the
- 56:38tax he gets exactly negative Q that's
- 56:41the full amount of Revenue raised right
- 56:43and he Bears all of that directly right
- 56:47but the consumer still loses the pass
- 56:51through rate times the quantity right
- 56:53because if this price Rises he's worse
- 56:55off and it will will typically rise
- 56:57right so the excess burden then is row *
- 57:02Q so everything the burden is fully
- 57:05borne by the monopolist and then it's
- 57:07additionally borne as excess burden by
- 57:09the
- 57:10consumer therefore the incidence the
- 57:12ratio of how much the consumer loses to
- 57:14how much the firm loses is the pass
- 57:16through rate divided by one or just the
- 57:18pass through rate right and again we can
- 57:20integrate this up as before to get the
- 57:22ratio of consumer to producer Surplus is
- 57:24the average pass through rate
- 57:28okay so just to see how this works
- 57:31here's a monopolist here's his marginal
- 57:33cost imagine now we shift up his
- 57:34marginal cost with a
- 57:36tax how much does he lose in profits
- 57:39well profits is the area between
- 57:40marginal revenue and marginal cost and
- 57:44that's Fallen by the quantity multiplied
- 57:47by the change right now there's a little
- 57:51extra triangle here but that's very
- 57:53small that's second order
- 57:56okay so um under uh under Monopoly the
- 58:03logic of incidence is therefore
- 58:05different in two ways so one is that
- 58:07there's this extra dead weight loss so
- 58:09that the incidence is not just split but
- 58:11there's this excess burden and the
- 58:13second thing is that the marginal
- 58:15revenue curve and not just the demand
- 58:17curve will help determine the pass
- 58:19through rate so now I want to consider
- 58:22uh P the pass through rate so Tanner
- 58:25very nice nicely derived from us for us
- 58:27the pass through rate under perfect
- 58:29competition let's do the same thing for
- 58:31Monopoly right for Monopoly marginal
- 58:33revenue is equal to marginal cost which
- 58:35also includes the tax so implicitly
- 58:38differentiating we get that marginal
- 58:39revenue Prime multiplied by the
- 58:42derivative of quantity with respect to
- 58:43the tax is equal to marginal cost Prime
- 58:46Times the derivative of quantity with
- 58:47respect to the tax plus
- 58:51one um and the derivative of quantity
- 58:55with respect to the tax is therefore
- 58:57equal to one over the derivative of
- 58:59marginal revenue minus the derivative of
- 59:01marginal
- 59:04cost um now how much does that lead to a
- 59:07change in price well how much does price
- 59:10change when quantity changes well it's
- 59:11just the derivative of price with
- 59:13respect to quantity and so the passive
- 59:15rate is p Prime over Mr Prime minus MC
- 59:19Prime now remember that Mr is equal to p
- 59:22+ P Prime * Q so if we let the marginal
- 59:26Surplus as we were talking about before
- 59:28equal to P Prime *
- 59:31q and we identify the marginal cost
- 59:34curve remember that the supply curve is
- 59:36just the inverse of the marginal cost
- 59:37curve so we can identify the supply
- 59:39curve with marginal cost
- 59:41curve then marginal cost Prime is equal
- 59:44to P over Q * the elasticity of supply
- 59:49just by the same logic we did to derive
- 59:52the elasticity of uh demand in the
- 59:55learner index before and P Prime is
- 59:57equal to P Q * elasticity of demand then
- 1:00:01we can replace all these terms with
- 1:00:03these
- 1:00:04here and we can divide through to give
- 1:00:07that the pass through rate is equal to 1
- 1:00:09over 1 plus the elasticity of demand
- 1:00:12minus one / the elasticity of supply
- 1:00:15Plus the one over the elasticity of the
- 1:00:17marginal Surplus function now this is
- 1:00:20basically similar to what we saw before
- 1:00:22right there's still 1 plus the
- 1:00:24elasticity of demand divided by the El
- 1:00:25elasticity of supply there's a negative
- 1:00:27one in here which is not all that
- 1:00:29important but the key new term is the
- 1:00:32one over the elasticity of the marginal
- 1:00:34Surplus
- 1:00:36function so the question is how should
- 1:00:38we interpret this elasticity of the
- 1:00:40marginal Surplus function Kim do you
- 1:00:42have any thoughts about
- 1:00:46that
- 1:00:49yeah anybody else like we we saw how the
- 1:00:53marginal Surplus function was behaving
- 1:00:55before
- 1:00:56right it was that area between the
- 1:00:58demand and the marginal revenue and we
- 1:01:00saw that it was doing different things
- 1:01:02depending on the demand curve that we
- 1:01:04looked
- 1:01:17at well so the El one over the
- 1:01:20elasticity of the marginal Surplus
- 1:01:23measures the curvature of
- 1:01:27demand it's going to be greater than one
- 1:01:32for concave demand how do we know that
- 1:01:34well remember as quantity was increasing
- 1:01:36that thing that that distance was
- 1:01:38increasing more than one for one when
- 1:01:41you had concave demand it wasn't just
- 1:01:43linearly increasing it was increasing at
- 1:01:46an increasing rate so that means it had
- 1:01:47an elasticity greater than one with
- 1:01:49linear demand it was increasing at a
- 1:01:51constant rate so that means it had an
- 1:01:53elasticity of one
- 1:01:55and for negative exponential demand it
- 1:01:57was completely constant so that mean it
- 1:01:59had zero elasticity right for log convex
- 1:02:03demands like the um the
- 1:02:07marginal uh like the constant elasticity
- 1:02:10demand it was it was actually decreasing
- 1:02:12and that means it has a negative
- 1:02:13elasticity right and if this is negative
- 1:02:17enough then the passor rate can even be
- 1:02:20infinite uh how do we know that well
- 1:02:23remember that in the inov at all example
- 1:02:27right we had that ironing line so that a
- 1:02:28small increase in marginal cost could
- 1:02:30lead to a discontinuous increase in
- 1:02:32price that's an infinite pass through
- 1:02:34rate and that came from the fact that
- 1:02:35that marginal Surplus was
- 1:02:38shrinking uh very quickly as the
- 1:02:42quantity was increasing right so in
- 1:02:46addition to the
- 1:02:48elasticities uh of demand and Supply we
- 1:02:51now are going to care about the
- 1:02:52curvature of demand as well
- 1:02:56um in particular when demand is concave
- 1:02:59when it's negatively curved the
- 1:03:01elasticity of marginal Surplus is going
- 1:03:03to be positive um and that's going to
- 1:03:06tend to make the um uh the pass through
- 1:03:11lower and when the elasticity and when
- 1:03:14the demand curve is convex it's going to
- 1:03:16tend to make the pass through much
- 1:03:18higher um now uh what are some ways that
- 1:03:23we might think about circumstances in
- 1:03:25which the curvature of demand might be
- 1:03:28positive or negative uh Kim do you have
- 1:03:30thoughts about
- 1:03:48that
- 1:03:50okay um well you can think of this as
- 1:03:53how much of the valuation is out in the
- 1:03:55tail
- 1:03:56so if inelastic demand really means
- 1:03:58people have spread out valuations for
- 1:04:00the thing uh curvature is really a
- 1:04:04measure of something like curtosis it's
- 1:04:06like how much is out in the Tails and in
- 1:04:07fact you can relate this to our Notions
- 1:04:09of fat taals before anytime you have fat
- 1:04:12tails and the fatter tails you have the
- 1:04:14more uh negative is going to be one over
- 1:04:18the elasticity of marginal
- 1:04:20Surplus um in fact the elasticity
- 1:04:23marginal Surplus is equal to the
- 1:04:24negative of that parameter Alpha that we
- 1:04:27had before and so 1 over negative Alpha
- 1:04:32is equal to this and so as you get
- 1:04:34towards Zip's law for example this is
- 1:04:36going to get very very uh
- 1:04:40large um so
- 1:04:42income uh tends so when income generates
- 1:04:46values when there's Goods that are
- 1:04:47valued more by the rich than they are by
- 1:04:49others and the more that they're more
- 1:04:50valued by the rich the more that this is
- 1:04:53going to be large or if the if a good
- 1:04:55very Niche appeal then this is going to
- 1:04:58be uh very large so let me give you um a
- 1:05:03graphical illustration of this so here's
- 1:05:06a concave demand function and here's its
- 1:05:10marginal revenue curve which is
- 1:05:12diverging at an increasing rate from the
- 1:05:14demand curve that means that for a small
- 1:05:17increase in marginal cost the increase
- 1:05:20in price is going to be much smaller
- 1:05:21because we move more up the marginal
- 1:05:23revenue curve than we do up the demand
- 1:05:25curve
- 1:05:27on the other hand when we have a
- 1:05:28constant elasticity demand like this
- 1:05:31because these are converging a small
- 1:05:33increase in the marginal cost curve
- 1:05:35leads us to move farther along the
- 1:05:37marginal revenue sorry farther along the
- 1:05:39demand curve than it does along the
- 1:05:41marginal revenue curve and therefore
- 1:05:42leads to twice as large of an increase
- 1:05:44in price as it did um an increase
- 1:05:48in uh uh marginal cost similarly changes
- 1:05:54in the shape of the marginal cost cost
- 1:05:56function which effectively changed the
- 1:05:58elasticity of supply will affect this as
- 1:06:00well so if we have a upward sloping
- 1:06:03marginal cost curve which makes you know
- 1:06:05somewhat inelastic supply then an
- 1:06:08increase in marginal cost leads to a
- 1:06:11smaller move in the quantities and
- 1:06:12therefore a small change in price
- 1:06:14whereas if you have declining marginal
- 1:06:16costs as you often do in natural
- 1:06:18monopolies then an increase that's like
- 1:06:20a negative elasticity of supply then an
- 1:06:22increase in marginal cost leads to a
- 1:06:24bigger change in quantities and
- 1:06:25therefore a bigger change in
- 1:06:28price okay that's it for today
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