清华大学中级微观经济学讲义(清华 李稻葵)3

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http:/// Chapter Three Preferences 消费者偏好

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Where Are We in the Course?We are studying the 1st of the three blocks of microeconomics: Consumer behavior, production theory, and market equilibrium Within the 1st block, we are working on the 2nd of the three components: choice set, preference, and consumer demand

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What Do We Mean by Preference? (偏好)It refers to the ordered relationship among alternative choices given by an economic agent. In most economic literature, consumer preference is treated as the ultimate exogenous element.

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Preference RelationsComparing two different consumption bundles, x and y: – strict preference: x is more preferred than is y. – weak preference: x is as at least as preferred as is y. – Indifference: x is exactly as preferred as is y.

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Notations denotes strict preference;

～ denotes indifference;

denotes weak preference; ~

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Preference Relationsx y and y x imply x ～ y.

~ ~ x y and (not y x) imply x ~ ~

y.

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Assumptions about Preference RelationsCompleteness: For any two bundles x and y it is always possible to make the statement that either x y ~ or y x.

~

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Assumptions about Preference RelationsReflexivity: Any bundle x is always at least as preferred as itself; i.e. x

x. ~

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Assumptions about Preference RelationsTransitivity: If x is at least as preferred as y, and y is at least as preferred as z, then x is at least as preferred as z; i.e. x

y and y z ~ ~

x z.

~

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Indifference Curves

无差异曲线 (或,无差异集)Take a reference bundle x’. The set of all bundles equally preferred to x’ is the indifference curve containing x’; the set of all bundles y ～ x’. Since an indifference “curve” is not always a curve a better name might be an indifference “set”.

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Indifference Curvesx2 x’ x” x”’ x1 x’ ～ x” ～ x”’

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Indifference Curvesx z z x

y x1

x2

y

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Indifference Curvesx2 I1 x I2 y z All bundles in I2 are strictly preferred to all in I3. x1 All bundles in I1 are strictly preferred to all in I2.

I3

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Indifference Curvesx2WP(x), the set of x bundles weakly preferred to x. WP(x) includes I(x) I(x).

x1

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Indifference Curvesx2SP(x), the set of x bundles strictly preferred to x, does not include I(x) I(x).

x1

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Indifference Curves Cannot Intersect ! (不相交!)x2 I1

I2 From I1, x ～ y. From I2, x ～ z. Therefore y ～ z.

x y z x1