Explain why indifference curves are usually drawn convex to the origin, are downward sloping and do not cross each other.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2019). The mark or mark type is shown in brackets.

1. [12] Explanation of diminishing marginal utility, and how more of a good is preferred to less of a good so the curves cannot cross; they have an 'indifferent' response along them representing a constant level of utility.
2. [9-12] L4: for a clear analysis of ICs and all three parts of the question.
3. [7-8] L3: for a less competent explanation of at least two of the parts of the question or a weaker explanation of all three parts.
4. [5-6] L2: for a competent explanation of one part or a weak explanation of two elements of the question.
5. [1-4] L1: for an answer that has some basic correct facts but includes irrelevancies and errors of theory.
6. [13] Theory states that consumers maximise satisfaction and determine demand by relating utility to price; this is shown by indifference curves and budget lines.
7. [13] Income changes shift budget lines parallel, price change of one good cause budget line to pivot.
8. [13] Equilibrium is changed – the extent and direction depending on the type of good.
9. [13] Explanation of income and substitution effects for an inferior good.
10. [9-13] L4: for a clear explanation of the links and correct analysis of income and substitution effects of price change.
11. [7-8] L3: for a briefer explanation; no clear link to the demand curve, or link to demand but some confusion over income and substitution.
12. [5-6] L2: for a poor explanation of the terms or a weak comment on the links.
13. [1-4] L1: for an answer that has some basic correct facts but includes irrelevancies and errors of theory.