CONSUMER BEHAVIOUR

CONSUMER’S EQUILIBRIUM–UTILITY MAXIMIZATION

The theory of demand starts with the examination of the behaviour of the consumers. In our everyday life we behave in different ways while buying and consuming a good or service. The simple calculations and human reasoning we undertake while doing any transactions have been transformed into principles which guide us to attain satisfaction or equilibrium in economic sense. When we go for shopping, we decide beforehand, what good to buy and how much to spend. It makes sense as we try to get most of what we are spending. In other words, we always want more of anything and for that purpose we negotiate and come to an agreed price which we are ready to pay happily. It is therefore, necessary to be first acquainted with the consumer behaviour, which forms the basis of the demand theory.

It is assumed that consumers are rational. Given his money income and the prices of commodities, a consumer always tries to maximize his satisfaction. That is, to get the maximum welfare (state of well-being) by spending the given money on various commodities. It is assumed that the satisfaction a consumer gets by consuming a good is measurable (measured in terms of money), though in real life it is not possible to measure satisfaction because it is psychological entity. We only feel the level of satisfaction and express the same in different ways. We show our satisfaction by our behaviour like laughing, jumping in excitement or in any other way. Thus, we cannot measure satisfaction in quantitative terms as we are capable of measuring time in seconds, weight in kilograms or length in meters. Further, each consumer is also assumed to be known of what he wants. Moreover, he has all information regarding market—the goods available, the prices of the goods at a particular point of time and so on. Every consumer uses this information in such a way as to maximize his total satisfaction.

To explain consumer’s equilibrium i.e., how a consumer attains maximum satisfaction by spending his money income on certain units of commodities, it is worthwhile to be familiar with certain important terms used in explaining various concepts and theories of demand. These are explained as under:

Utility

Utility is defined as the power of a commodity or service to satisfy a human want. Economists have leveled the term satisfaction as utility. It is subjective concept and therefore varies from person to person. As already stated, it resides in one’s mind and therefore cannot be measured in quantitative terms. Though utility and satisfaction are used synonymously, we should note that utility is the expected satisfaction whereas satisfaction implies ‘realized satisfaction’.

Total Utility

It is the amount of utility (satisfaction); a consumer gets by consuming all the units of a commodity. If there are n units of the commodity then the total utility is the sum of the utilities of all n units of the commodity. Thus, if there are four units of a commodity, then total utility is,

U = U₁(n₁) + U₂(n₂) + U₃(n₃) + U₄(n₄)

Where U = total utility; U₁…….U₄ are the utilities of n₁…..n₄ units of the commodity.

Thus, if by consuming first apple, a consumer gets 12 utils of satisfaction, 10 utils from the second apple, 9 utils from the third and 7 utils from the fourth apple; then his total utility is,

U = 12 + 10 + 9 + 7 = 38

Thus utilities of various goods are additive. This means that utilities of different commodities are independent of one another. The utility derived from one commodity does not affect that of another.

Marginal Utility

Marginal utility is defined as the change in the total utility due to a unit change in the consumption of a commodity per unit of time. It can also be defined as the addition made to the total utility by consuming an additional unit of a commodity. For example, if total utility of 3 cups of tea is 18 utils and on consuming the 4^th cup it rises to 20; then marginal utility 20-18 = 2 utils. Thus, by consuming one more cup of tea, the additional utility, a consumer gets is 2 utils. Marginal utility can be expressed as,

∆TU

MU =  ^∆

Q

Where MU = marginal utility; ∆ΤU = change in total utility; ∆Q = change in the quantity consumed. ‘Utils’ is the term used by Marshall as a measuring unit of utility. The following expression can also be used to find marginal utility:

MU = TU_n  – TU_n-1

Where, TU_n is the total utility of nth unit of the commodity and TU_n-1 utility from the n-1th commodity. Thus, if TU from the second unit (nth unit) of apple is 13 and TU from the previous unit (n-1) is 7, then MU is 13 – 7 = 6.

The concept of total utility and marginal utility is shown in the utility schedule below:

Units of apples	Total utility	Marginal Utility
1	7	7 – 0 = 7
2	13	13 – 7 = 6
3	18	18 – 13 = 5
4	22	22 – 18 = 4
5	25	25 – 22 = 3
6	27	27 – 25 = 2
7	28	28 – 27 = 1
8	28	28 – 28 = 0

When the consumer takes 1^st apple, his total utility is 7 and from the 2^nd apple he gets 13 and so on. The third column shows marginal utility, which diminishes as the consumer increases units of apples. It is seen that when total utility is maximum, marginal utility is zero at 8^th unit of apple. It is also seen that total utility is the sum of the marginal utilities of the 1^st, 2^nd, 3^rd, and so on. Thus, at 8^th unit of apple,

TU = MU₁ + MU₂ + MU₃ + MU₄ +…..…+ MU_n(8)

i.e. 28 = 7 + 6 + 5 + 4 +…..…+ 0

LAW OF DIMINISHING MARGINAL UTILITY

One of the very important laws in regard to the satisfaction of human wants is known as law of diminishing marginal utility. The law explains common feeling of every consumer. Suppose a person starts consuming apples one after another. The first apple gives him the maximum satisfaction as he might be in mood of taking some food at that time for meeting his appetite. As he takes the second apple, he gets less satisfaction because by this time he has already met some level of appetite. The third and more apples yield him lesser satisfaction or utility. It means that every time the consumer increases his consumption, he gets less and less satisfaction. The satisfaction also tends to be zero when the consumer feels totally disgusted to take any more apples. If he takes more, his satisfaction turns negative or utility now becomes disutility.

Thus law of diminishing marginal utility states that additional satisfaction a person derives by consuming a commodity goes on declining as he consumes more and more of a that commodity. According to Marshall, “The additional benefit which a person derives from a given increase of his stock of a thing diminishes with every increase in stock that he already has.”

Two important reasons for diminishing marginal utility are the following:

(a) Each particular want is satiable (can be satisfied): Though there are unlimited wants, a single want can be satisfied. Thus, when a consumer consumes more and more of a commodity, his want is satisfied and he does not wish to have any further increase in the commodity. As such his marginal utility falls when consumption increases.

(b) Goods are imperfect substitutes for one another i.e., one good cannot be exactly used in place of another: Satisfaction from any two goods is not same. Different goods satisfy different wants. If a good could be perfectly substituted for another, it would have satisfied other wants. Hence, its marginal utility would not have fallen but increased.

The law can be explained with the help of a table and diagram-3.1 below:

Units (Apples)	TU	MU
1	10	10
2	18	8
3	22	4
4	24	2
5	25	1
6	25	0
7	32	–7
8	44	–12

As the consumer goes on consuming more and more units of apples, total utility (TU) increases but marginal utility (MU) declines continuously and becomes zero at 6^th unit. When consumer consumes further, utility becomes negative. It is to be noted that when TU is maximum, MU is zero. Let us now derive the MU curve from the above schedule as under. Marginal utility is measured along Y-axis while units of apples along X-axis. MU is the marginal curve falling downwards from left to right. This is diminishing MU curve. It is seen in the Fig. 3.1 below, that marginal utility is zero when the consumer buys 6^th apple. As he consumes more, marginal utility becomes negative.

The law of diminishing MU has certain limitations. These are:

1.        If units of a commodity consumed are not of same size and shape, the law does not hold good. In the illustration explained above, units of apples are assumed to be of same shape and size.

2.     The law does not hold good when there is enough time gap between consumption of two units. For instance, if we take second apple after a long gap of time, we may feel hungry and hence satisfaction will increase instead of falling.

3.     The taste of consumer should not change for the law to hold good. It means that the person should consume all units of a good by same desire and pleasure.

4.     The law does not apply to money as it is said that more money a person has, the more he wants.

5.     Change in income of the consumer will falsify the law. If money income of the consumer increases or decreases during the time of consumption of a particular set of goods, the marginal utility will not fall as said above.

The law of diminishing marginal (additional) utility explains consumer’s equilibrium in case of a single commodity. A consumer will go on purchasing successive units of a commodity till the marginal utility of the commodity is equal to price. Thus, for a single commodity x, a consumer is in equilibrium when the marginal utility of x is equal to its market price (P_x). Symbolically,

MU_x  = P_x

In case the price goes down, he will buy more and the marginal utility will come down to the level of price. If price rises, less will be purchased and the marginal utility rises till it reaches the new level of price. Thus, equality between marginal utility and price indicates the position of consumer’s equilibrium when a single commodity is being purchased and consumed.