A fixed basket, a higher nominal income and a misleading headline

A classroom dataset follows a fixed basket containing two units of product A and one unit of product B. In the base periodA costs 3 and B costs 4 currency units. In the comparison periodA costs 4 and B costs 5. A household’s nominal income rises from 1,000 to 1,040 over the same interval. A headline says that income has increased, so the household can certainly afford more of everything. The students must calculate the supplied fixed-basket index and the corresponding base-price income measure before assessing that claim. They also receive a voluntary web survey in which most responses come from one affluent neighborhood, while areas with poor internet access contribute very few. The task is to distinguish an arithmetic result for this particular basket from an unsupported statement about every household, every product and the representativeness of a survey.