T DEALLY, to determine the extent to which persons of a particular income group spend an increment to income, time series data on consumption and disposable income for individual households (panel data) are needed. Unfortunately, such data are not available. Available are time series aggregate data, which do not allow one to determine differential marginal propensities to consume for different income groups, and cross section data which do not allow one to trace over time the effects of changes in income on consumption. However, by utilizing both time series and cross section data, the hypothesis that the marginal propensity to consume decreases as income increases can be tested.