lecture 1: the market and consumer theory
TRANSCRIPT
Lecture 1: The market and consumer theory
Intermediate microeconomics
Jonas Vlachos
Stockholms universitet
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The market
β’ Demand
β’ Supply
β’ Equilibrium
β’ Comparative statics
β’ Elasticities
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Demand
β’ Demand function. Mathematical relation between quanitity
demanded (Qd), own price (p) and other factors
β’ For example
β’ Where p is own price, pb and pc are prices of substitutes,
and Y is income
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Demand curve: own price change
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Holding everything but own price equal
Movement along the demand curve
dQ/dp=-20 (million kg/$)
Since p is on y-axis, slope=1/(dQ/dp)=dp/dQ=-0.05
($/million kg)
Demand curve: changes in other
prices or income
Increases in substitute goods or income shifts the
demand curve
At any given price of pork, demand for pork increases
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Supply
β’ Supply function: mathematical relation between
quantity supplied (QS), own price (p) and other factors
(for example input prices)
β’ For example
Where p is own price and ph is input price
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Supply curve: own price change
Holding everything but own price equal
Movement along the supply curve
dQ/dp=40 (million kg/$)
Since p is on y-axis, slope=1/(dQ/dp)=dp/dQ=0.025
($/million kg) 7
Supply curve: increase in input price
Shifts the supply curve
At any given pork price, less is supplied
8
Market equilibrium: demand=supply
Qd = 286-20p = QS = 88+40p => Q = 220
Since Q = 220, p = 3.3
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Comparative statics: large shocks
What happens when some βshockβ affects the demand or
supply of a good?
For example: large increase in input price, from 1.5 to 1.75
Previous: QS = 88+40p. Now: QS = 73+40p
10
55.3$
407320286
p
pp
QQsd
21555.320286 d
Q
21555.34073 s
Q
Comparative statics: small shocks
Demand is a function of price, holding everything else
constant: Q = D(p)
Supply is a function of price and some exogenous factor a.
(exogenous here means βoutside the control of firmsβ)
Q = S(p,a)
Prices will indirectly depend on a, so in equilibrium:
D(p(a)) = S(p(a),a)
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Comparative statics: small shocks
To analyze the impact of a small change in a (for example
input price), use the chain rule when differentiating the
equilibrium condition with respect to a
Rearrange:
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<0
>0 <0
>0 (equilibrium prices increase
when a increases)
Elasticities
How responsive is a variable to a change in another variable?
Price elasticity of demand:
Price elasticity of supply:
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Elasticity: example with linear demand
14
Linear demand: Qd = a-bp => dQ/dp=-b
ν =
ππ
ππ
π
π= βπ
π
π
Constant elasticity demand curves
(Q = ApΞ΅)
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Constant elasticity supply curves
(Q = BpΞ·)
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Consumer theory
β’ The demand function builds on assumptions concerning
consumer preferences
β’ Consumers also face constraints
β’ Also assume that consumers try to do as well as they
can, that is maximize their well-being
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Preferences: notation
β’ Consumers have preferences over βbundlesβ of
goods and services
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Strict preference. E.g. a b (a is better than b)
Weak preference. Bundle a is at least as good as b
~ Indifference. Bundle a exactly as good as b
Preferences: basic assumptions
β’ Completeness: all bundles can be ranked
a consumer can rank them so that either a b,
b a, or a ~ b
β’ Transitivity:
Consumersβ rankings are logically consistent in the
sense that if a b and b c, then a c.
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Well behaved preferences
β’ Non-satiation
(monotonicity):
β More is better
β’ Convexity:
β Averages are prefered to
extremes
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From preferences to indifference curves
Consider combinations of two possible goods. The bundles that
make a consumer equally happy make up indifference curves
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Indifference curves
β’ The preference assumptions imply certain properties for
indifference curves
β Every bundle is on an indifference curve (completeness)
β Indifference curves further from the origin are better (non-
satiation)
β Indifference curves cannot cross (transitivity)
β Indifference curves cannot slope upwards (non-satiation)
β Indifference curves cannot be thick (non-satiation)
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Indifferences curves cannot cross
Y ~ Z
Z ~ X
But
Y ~ X
Transitivity violated
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/
From preferences to utility and utility
functions
β’ Utility is an analytical tool to describe preferences
β’ Ordinal: utility only describes how bundles are ranked
relative to each other
β Not a cardinal measure that tells us by how much bundles are
preferred
β’ A utility function assignes a larger value to the more
prefered bundle, but units to not matter
β If x y, then u( ) is a utility function if u(x) > u(y)
β’ A utility function can be transformed into another utility
function such that the preference ordering is maintained
β Positive monotonic transformation 24
Compare to temperatures
Celsius Fahrenheit Kelvin
50 122 323
100 212 373
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Describe the same temperature relation, but units differ
Marginal rate of substitution (MRS)
MRS is the amount of one good that an individual is willing to give
up for another good for any given utility level: MRS = dq2/dq1
Marginal utility is the increase in utility that a consumer gets from
consuming the last unit of a good, holding other consumption
constant: πΏπ
πΏπ1= π1
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Different preferences => different utility
functions => different MRS:s
We often assume that goods are imperfect substitues, but
that is not necessary
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Indifference curves
Perfect subsitutues and perfect complements are βextremesβ,
many different standard, convex, utility functions
Cobb-Douglas never hit the axis
Quasi-linear hit one of the axis
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Some commonly used utility functions
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The budget constraint: basics
Consumers maximize utility, subject to constraints
Given prices p1, p2, and income Y, the budget line is
If p1 = $1 p2 = $2 and Y = $50, the budget line is:
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The budget constraint: MRT
The marginal rate of transformation, MRT, tells how the market
allows a consumer to trade (βtransformβ) one good for another
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Constrained consumer choice
Maximize utility subject to the budget constraint
Given βstandardβ indifference curves, there is an interior
optimum. The highest feasible indifference curve.
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Maximizing utility using calculus: I
One way to solve consumer maximization is to directly
assume an interior solution and thus MRS=MRT (here
Cobb-Douglas utility)
maxπ,π
π(π, π) = ππΌπ1βπΌ subject to π = πππ + πππ
πππ =πΏπ(π, π)
πΏπ= πΌππΌβ1π1βπΌ
πππ =πΏπ(π, π)
πΏπ= (1 β πΌ)ππΌπβπΌ
ππ πππ =
πππ
πππ=
πΌππΌβ1π1βπΌ
(1 β πΌ)ππΌπβπΌ=
πΌ
1 β πΌ
π
π=
ππ
ππ= ππ π
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Maximizing utility using calculus: I (cont)
From this we see that
π =
(1 β πΌ)ππ
πΌ πππ, where
(1 β πΌ)ππ
πΌ ππ is a constant.
We now have the optimal allocation between Z and X, but how much we
consume also depends on income Y. Insert expression for Z in the budget
constraint
π = πππ + ππ
(1 β πΌ)ππ
πΌ πππ = πππ 1 +
1 β πΌ
πΌ= πππ
πΌ
πΌ+
1 β πΌ
πΌ=
ππ
πΌπ β
πβ =πΌπ
ππ (optimal quantity of X). Continuing for Z, we get
πβ =(1 β πΌ)ππ
πΌ πππβ =
(1 β πΌ)ππ
πΌ ππ
πΌπ
ππ=
1 β πΌ π
ππ (optimum quatity of Z)
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Maximizing utility using calculus: II
The Lagrangian method: optimization with constraints
General: maximize f(x) + Ξ»g(x)
Maximize π π1, π2 subject to π = π1π1 + π2π2
Chose optimal values of q1, q2, and Ξ»
Think of Ξ» as the cost of violating the constraint
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Maximizing utility using calculus: II
Find first order conditions:
Equating (1) and (2) conditions yields
Ξ» is the marginal utility of income (βshadow valueβ of income)
The value of relaxing the constraint
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(1)
(2)
(3)
Special case 1: Perfect complements
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Special case 2: Perfect substitutes
If the marginal rate of substitution is not equal to
the marginal rate of transformation, you will only
chose the relatively cheap good. Corner solution
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Special case 3: Quasilinear preferences
Under quasilinear preferences, the price of one good may be
so high that you do not consume any of it. Corner solution
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Expenditure minimization
An alternative approach to consumer optimization is to
consider the lowest cost at which you can achieve a certain
level of utility. I.e. to mimimize expenditures
The solution gives you the expenditure function, the
minimum expendtures needed to achive a certain utility
level
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Are the basic assumptions correct?
β’ Behavioural economics analyses the basic rationality
assumptions. Numerous deviations recorded
β Endowment effects: what people actually own affects their
preferences
β Salience: people do not (fully) incorporate costs such as
taxes when making economic decisions
β Transitivity: basically seems to hold
β’ But, we are working with models
β The economic importance of such deviations is not fully
understood
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