Theory of Consumption - Revealed Preference Analysis

Introduction: In 1960 Mr. Samuelson introduced the Revealed Preference Analysis to explain the behaviour of the consumer. The fundamental difference between the Utility Analysis, Indifference Curve Analysis and Revealed Preference Analysis is that when the first two are based on the psychology of the consumer, the revealed Preference is based on the actual behaviour of the consumer.

Assumptions: In order to explain the behaviour of the consumer with the help of Revealed preference Analysis, Mr. Samuelson made the following assumptions.

1. Utility cannot be measured.

2. The consumer always prefers more of a good to less, until his income is exhausted.

3. It is based on the Principle of Strong Ordering. This means that if the consumer is given many commodities, he can place them in order of his preference.

4. It is based on the Principle of Consistency, and the consumer acts consistently. 'Consistency in choice' means that if the consumer chooses the commodity combination P in preference to all other combinations, then he will never subsequently choose any combination from the rejected ones in a situation in which P is also available. This is the key to this approach.

5. The choice made by the consumer will reveal the preference of the consumer for the commodity. If he chooses P over Q, then this choice reveals his preference for P.

6. The consumer's preference pattern maintains transitivity. If the consumer prefers P over Q, and Q over R, Then he definitely prefers P over R.

The substitution effect is always non-positive. It can never result into a reduction in the purchase of the commodity whose price has fallen.

In order to find out the consumer's equilibrium position with the Revealed Preference Analysis, we make the following assumptions.

1. The consumer has a fixed amount of income.
2. There are only two commodities available in the market, namely A and B.

On the basis of these assumptions we can now draw the following diagram and find out the consumer's equilibrium position.

Let us assume that the price line or budget line is XY. It represents all combinations of commodities A and B available to the consumer. The consumer can choose any of the combinations of commodities A and B, lying within, or on border of the shaded triangle OXY.
We now assume that out of all the combinations available to him, the consumer chooses to consume Oa of commodity A and Ob of commodity B. This combination is represented by the point P. Thus the consumer has chosen the combination P in preference to all other combinations lying within the triangle OXY. So in future he will never choose any combination from triangle OXY in a situation where P is also available.

Now there is a fall in the price of commodity B. The price of commodity A and the income of the consumer remains constant. Given the same income, the consumer can still consume OX of commodity A by spending all his income on commodity A. Also as the price of commodity B has fallen, he can consume OZ of commodity B instead of Ob, by spending all his income on commodity B. Therefore, XZ is the new budget line.

A fall in the price of a commodity is equivalent to an increase in real income. This income effect needs to be eliminated. This is done by moving the new budget line XZ towards the origin O, keeping it parallel to its original position, until it passes through point P. So the new budget line is X'Z', where the consumer is able to purchase his original combinations of commodities A and B at P, but at the new set of prices. (new price for commodity B only; price of commodity A has not changed). The consumer can now choose any point on X'Z'.

Considering the segment X'P: All points on segment X'P were available to the consumer before the fall in the price of commodity B. All these points were within the triangle OXY and rejected by him originally in favour of the combination at point P. So, in the new situation, where P is still available, he will definitely choose P rather than a combination previously rejected. This is because the consumer moves according to the Principle of Consistency.

Considering the segment PZ': The segment PZ' represents combinations of commodities which were not previously available to the consumer. It would therefore be quite consistent for the consumer to choose some combination along the PZ' part of the new budget line. This could mean consuming more of commodity B, whose price has fallen.

This implies that the consumer either consumes same quantity of commodity B as before by remaining at point P, or more of the commodity B by choosing a point on the segment PZ'. The consumer selects the point Q. If we now restore the income effect and return to the changed budget line XZ, the consumer will move to R on the changed budget line XZ, as a result of both income effect and substitution effect, where bc (the price effect) = bs (the substitution effect) + sc (the income effect).

Conclusion: The substitution effect can never lead the consumer to buy less of a commodity whose price has fallen.

Unless the income effect is negative and of sufficient magnitude to neutralize the substitution effect, under the assumption of consistency in choice, the demand curve of a consumer for any product will slope downward to the right.

Criticism: Some economists have said that this analysis is based on the assumption of Strong Ordering. But according to the critics if the consumer is given many commodities it will not be possible for him to follow the Principle of Strong Ordering. In the case of many commodities there may be a stage where the consumer will be indifferent.

Though there are some defects in this analysis, the advocates of this analysis regard this as superior to the other two because it is based on the actual behaviour of the consumer. So according to them this is more scientific because it is based on the actual behaviour of the consumer.