This paper argues that the collapse of stock prices in October 1929 generated temporary uncertainty about future income which led consumers to forgo purchases of durable goods. That the Great Crash generated uncertainty is evidenced by the decline in surety expressed by contemporary forecasters. That this uncertainty affected consumer behavior is shown by the fact that spending on consumer durables declined drastically in late 1929, while spending on perishable goods rose slightly. This effect is confirmed by the fact that there is a significant negative relationship between stock market variability and the production of consumer durables in the prewar era. "Uncertainty is worse than knowing the truth, no matter how bad"

There is a tendency to think of official government statistics as unambiguous measures of economic activity. In truth, however, nearly all of the available series are based heavily on assumptions, and are sensitive to the estimation techniques used. Furthermore, many of these assumptions and estimation techniques have been refined and improved over time. Whether these underlying assumptions are reasonable and whether the refinement of assumptions over time has been useful depends crucially on the questions one is trying to answer. For example, an estimate of consumption derived from data on retail sales may be perfectly adequate for planning future production, or setting government budgets, but may be disastrous for testing a subtle economic theory. Similarly, gathering more genuine consumption data might improve our current estimates of consumption, but a series that reflects retail sales for one era and genuine consumption for another could wreak havoc when used in estimating a time-series rela