This paper starts with some reflections on the notion of the representative consumer. These reflections result in the conclusion that the "average consumer" is - in general - not a representative consumer in the sense that he may be considered as a (fictitious) consumer acting in the same way as the individual consumers are supposed to do, i.e. maximizing their utility subject to a budget constraint. Nevertheless, relations between per capita consumption on the one hand and income and prices on the other hand, may be such that, though being non-linear in income, they are "aggregation consistent". This is at the cost of more information on incomes. Here we used a time series of the coefficients of variation of the income distribution in the Netherlands, leading to a Quadratic Engel Curve (Q.E.C.) demand system.