a primer on consumer choice preferences, indifference curves and utility
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Lecture 10 slide 1
A primer on
Consumer ChoicePreferences, Indifference Curves and
Utility
Lecture 10 slide 2
INTRODUCTION
PreferencesIndifference CurvesUtility
Lecture 10 slide 3
The problem
Simplify the consumer’s choice problem into her making the best she can to maximize her satisfaction
Lecture 10 slide 4
Preferences
What is best? We assume that what is best for the consumer
should be left to her to decide (we want to be positive, not normative)
And that her preferences, how much she enjoys the consumption of goods can be described by using indifference maps
Lecture 10 slide 5
Preferences
Define a consumption bundle (or basket) as a combination of quantities of different goods (for simplicity 2 goods)
Say we use goods X and Y so the basket is (x,y)
Lecture 10 slide 6
Properties of Preferences
We assume preferences to be:complete: any bundle (x,y) can be compared to any
other bundle (x’,y’), the consumer can rank them or know that she is indifferent between both
This might seem rational…but not always, …like when you are 4 years old and your brother is 5 or so :)
- Ýx,yÞ, Ýxv,yvÞ Ýx,yÞOÝxv,yvÞ or Ýxv,yvÞOÝx,yÞ or both: Ýxv,yvÞ i Ýx,yÞ
Lecture 10 slide 7
Properties of Preferences
We assume preferences to be:transitive: if (x,y) is weakly preferred to (x’,y’) and
(x’,y’) is weakly preferred to (x”,y”) then the consumer must weakly prefer (x,y) to (x”,y”)
- Ýx,yÞ, Ýxv,yvÞ,Ýxvv,yvvÞÝx,yÞP Ýxv,yvÞ , Ýxv,yvÞP Ýxvv,yvvÞ => Ýx,yÞP Ýxvv,yvvÞ
Lecture 10 slide 8
Properties of Preferences
We assume preferences to respect the non-satiation property (for the case of goods) or free disposability
- Ýx,yÞ,Ýxv,yvÞx > xv,y ³ yv=> Ýx,yÞÉ Ýxv,yvÞ
Lecture 10 slide 9
Indifferences curves
We can represent the preferences of consumers by using indifference curves
These show in the x, y space those consumption bundles about which the consumer is indifferent
Indifference curve: combinations of goods that give the same level of satisfaction
We are going to think of X and Y as pizzas and burritos and of x and y as pizzas per semester and burritos per semester
Lecture 10 slide 10
Indifferences curves
Using the property of nonsatiation, we can work out the green area of preferred bundles and the orange area of dominated bundles
Lecture 10 slide 11
Indifferences curves
The indifference curve passing through e might well look like this (it respects the nonsatiation property)
Lecture 10 slide 12
Indifferences curves
The further from the origin, the more utility the indifference curves show
y
x
Better
Lecture 10 slide 13
Indifferences curves
There is an indifference curve through all possible bundles
y
x
Lecture 10 slide 14
Indifferences curves
Indifference curves cannot cross!
y
x
eb
a
Lecture 10 slide 15
Indifferences curves
Indifference curves cannot be any thick!
y
x
eb
Lecture 10 slide 16
Indifferences curves
Indifference curves for goods should slope downwards
y
x
e
b
Lecture 10 slide 17
Marginal Rate of SubstitutionIndifference curves tell us about the willingness of the consumer to substitute one good for the other
y
x
e
b
Lecture 10 slide 18
Marginal Rate of Substitution
The Marginal Rate of Substitution is the maximum amount of one good the consumer is willing to sacrifice to obtain a marginal unit of the other good
y
x
e
b
MRS is the slope of the indifference curve
Lecture 10 slide 19
The curvature of indifference curves
Most indifference curves are convex to the origin, exhibiting decreasing MRS between the goods
y
x
e
b
Lecture 10 slide 20
The curvature of indifference curves
But other possibilities exist: concave curves (increasing MRS!!!) => you prefer the extremes to the mixing, perhaps you hate the combination of both goods! Or they are individually addictive…
y
x
e
b
Ice-cream
anchovies
Lecture 10 slide 21
The curvature of indifference curves
But other possibilities exist: straight lines =>what kind of preferences do they represent?
y
x
e
b
Lecture 10 slide 22
The curvature of indifference curves
Check the slope…constant what does it show?
y
x
e
bGo to hidden slide
Lecture 10 slide 24
The curvature of indifference curves
What about this slope?
y
x
e
bGo to
hidden slide
Lecture 10 slide 26
The curvature of indifference curves
What about this shape?
y
x
e
bGo to
hidden slide
Lecture 10 slide 28
The curvature of indifference curves
These goods have A different complementarily ratio
Sugarcubes
Tea cups
e
b
Lecture 10 slide 29
The curvature of indifference curves
What about this shape? Could happen with food and clothes
y
x
Lecture 10 slide 30
Next
Utility and Budget Constraints
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