Consumption function

In economics, the consumption function describes a relationship between consumption and disposable income.[1][2] The concept is believed to have been introduced into macroeconomics by John Maynard Keynes in 1936, who used it to develop the notion of a government spending multiplier.[3]

Graphical representation of the consumption function, where a is autonomous consumption (affected by interest rates, consumer expectations, etc.), b is the marginal propensity to consume and Yd is disposable income.

Details

Its simplest form is the linear consumption function used frequently in simple Keynesian models:[4]

C=a+b\times Y_{d}

where $a$ is the autonomous consumption that is independent of disposable income; in other words, consumption when income is zero. The term $b\times Y_{d}$ is the induced consumption that is influenced by the economy's income level. It is generally assumed that there is no correlation or dependence between $Y_{d}$ and C.

The parameter $b$ is known as the marginal propensity to consume, i.e. the increase in consumption due to an incremental increase in disposable income, since $\partial C/\partial Y_{d}=b$ . Geometrically, $b$ is the slope of the consumption function. One of the key assumptions of Keynesian economics is that this parameter is positive but smaller than one, i.e. $b\in (0,1)$ .[5]

Keynes also took note of the tendency for the marginal propensity to consume to decrease as income increases, i.e. $\partial ^{2}C/\partial Y_{d}^{2}<0$ .[6] If this assumption is to be used, it would result in a nonlinear consumption function with a diminishing slope. Further theories on the shape of the consumption function include James Duesenberry's (1949) relative consumption expenditure,[7] Franco Modigliani and Richard Brumberg's (1954) life-cycle hypothesis, and Milton Friedman's (1957) permanent income hypothesis.[8]

Some new theoretical works following Duesenberry's and based in behavioral economics suggest that a number of behavioural principles can be taken as microeconomic foundations for a behaviorally-based aggregate consumption function.[9]

Notes

Algebraically, this means $C=f(Y_{d})$ where $f\colon \mathbb {R} ^{+}\to \mathbb {R} ^{+}$ is a function that maps levels of disposable income $Y_{d}$ —income after government intervention, such as taxes or transfer payments—into levels of consumption $C$ .
Lindauer, John (1976). Macroeconomics (Third ed.). New York: John Wiley & Sons. pp. 40–43. ISBN 0-471-53572-9.
Hall, Robert E.; Taylor, John B. (1986). "Consumption and Income". Macroeconomics: Theory, Performance, and Policy. New York: W. W. Norton. pp. 63–67. ISBN 0-393-95398-X.
Colander, David (1986). Macroeconomics: Theory and Policy. Glenview: Scott, Foresman and Co. pp. 94–97. ISBN 0-673-16648-1.
Keynes, John M. (1936). The General Theory of Employment, Interest and Money. New York: Harcourt Brace Jovanovich. p. 96. The fundamental psychological law ... is that men [and women] are disposed, as a rule and on average, to increase their consumption as their income increases, but not as much as the increase in their income.
Keynes, John M. (1936). The General Theory of Employment, Interest and Money. New York: Harcourt Brace Jovanovich. The marginal propensity to consume is not constant for all levels of employment, and it is probable that there will be, as a rule, a tendency for it to diminish as employment increases; when real income increases, that is to say, the community will wish to consume a gradually diminishing proportion of it.
Duesenberry, J. S. (1949). Income, Saving and the Theory of Consumer Behavior.
Friedman, M. (1957). A Theory of the Consumption Function.
d’Orlando, F.; Sanfilippo, E. (2010). "Behavioral foundations for the Keynesian consumption function". Journal of Economic Psychology. 31 (6): 1035. doi:10.1016/j.joep.2010.09.004.

External links

An essay examining the strengths and weaknesses of Keynes's theory of consumption

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[1] Algebraically, this means $C=f(Y_{d})$ where $f\colon \mathbb {R} ^{+}\to \mathbb {R} ^{+}$ is a function that maps levels of disposable income $Y_{d}$ —income after government intervention, such as taxes or transfer payments—into levels of consumption $C$ .

[2] Lindauer, John (1976). Macroeconomics (Third ed.). New York: John Wiley & Sons. pp. 40–43. ISBN 0-471-53572-9.

[3] Hall, Robert E.; Taylor, John B. (1986). "Consumption and Income". Macroeconomics: Theory, Performance, and Policy. New York: W. W. Norton. pp. 63–67. ISBN 0-393-95398-X.

[4] Colander, David (1986). Macroeconomics: Theory and Policy. Glenview: Scott, Foresman and Co. pp. 94–97. ISBN 0-673-16648-1.

[5] Keynes, John M. (1936). The General Theory of Employment, Interest and Money. New York: Harcourt Brace Jovanovich. p. 96. The fundamental psychological law ... is that men [and women] are disposed, as a rule and on average, to increase their consumption as their income increases, but not as much as the increase in their income.

[6] Keynes, John M. (1936). The General Theory of Employment, Interest and Money. New York: Harcourt Brace Jovanovich. The marginal propensity to consume is not constant for all levels of employment, and it is probable that there will be, as a rule, a tendency for it to diminish as employment increases; when real income increases, that is to say, the community will wish to consume a gradually diminishing proportion of it.

[7] Duesenberry, J. S. (1949). Income, Saving and the Theory of Consumer Behavior.

[8] Friedman, M. (1957). A Theory of the Consumption Function.

[9] ’Orlando, F.; Sanfilippo, E. (2010). "Behavioral foundations for the Keynesian consumption function". Journal of Economic Psychology. 31 (6): 1035. doi:10.1016/j.joep.2010.09.004.

Consumption
Topics	Consumption function Final consumption expenditure Instant gratification Intertemporal consumption Random walk hypothesis Autonomous consumption Induced consumption Conspicuous consumption
Theories	Absolute income hypothesis Life-cycle hypothesis Permanent income hypothesis Random walk model of consumption Relative income hypothesis
Lists	List of largest consumer markets

Consumer behaviour
Concepts	Consumption Autonomous consumption Induced consumption Consumer culture theory Consumer debt Consumer economy Consumer spending
Research types	Consumer behaviour Consumer choice Consumer economics Consumer neuroscience Consumer product Marketing research
Consumer attributes	Consumer confidence Consumer confusion Consumer ethnocentrism Consumer socialization Consumer's risk Consumption function Cultural consumer Homo economicus
Processes	Consumers' co-operative Consumer-to-business Factory-to-consumer Consumer service Consumerization

Consumption function

Details

See also

Notes

Further reading

External links