CHAPTER 3 Consumer Preferences and Choice

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CHAPTER 3 Consumer Preferences and Choice 67
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FIGURE 3.5 Some Unusual Indifference Curves Horizontal indifference curves,
as in the top left panel, indicate that X is a neuter; that is, the consumer is indifferent
between having more or less of it. Vertical indifference curves, as in the top right
panel, would indicate instead that commodity Y is a neuter. Indifference curves that
are negatively sloped straight lines, as in the bottom left panel, indicate that MRSXY is
constant, and so X and Y are perfect substitutes for the individual. The bottom right
panel shows indifference curves that are concave to the origin (i.e., MRSXY increases).
Finally, the bottom right panel shows indifference curves that are concave rather than
convex to the origin. This means that the individual is willing to give up more and more
units of good Y for each additional unit of X (i.e., MRSXY increases). For example,
between points A and B on U1, MRSXY = 2/2 = 1; between B and C, MRSXY = 3/1 = 3;
and between C and F, MRSXY = 3/0.5 = 6. In Section 3.5, we will see that in this unusual
case, the individual would end up consuming only good X or only good Y.
Even though indifference curves can assume any of the shapes shown in Figure 3.5,
they are usually negatively sloped, nonintersecting, and convex to the origin. These characteristics
have been confirmed experimentally. 9 Because it is difficult to derive indifference
curves experimentally, however, firms try to determine consumers’ preferences by
marketing studies, as explained in Example 3–2.
9 See, for example, K. R. MacCrimmon and M. Toda, “The Experimental Determination of Indifference
Curves,” Review of Economic Studies, October 1969.