Friedman's Permanent Income Hypothesis
After the Second World War, it was noticed that a model in which current consumption was just a function of current income clearly too simplistic. It could not explain the fact that the long-run average propensity to consume seemed to be roughly constant despite the marginal propensity to consume being much lower. Friedman's Permanent Income Hypothesis are one of the models which seeks to explain this apparent contradiction.
According to the Permanent Income Hypothesis, permanent consumption, CP, is proportional to permanent income, YP. Permanent income is a subjective notion of likely medium-run future income. Permanent consumption is a similar notion of consumption.
Actual consumption, C, and actual income, Y, consist of these permanent components plus unanticipated transitory components, CT and YT, respectively.
CPt =β2YPt
Ct = CPt + CTt
Yt = YPt + YTt
Read more about this topic: Intertemporal Choice
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