Good quality data is paramount for applied economic research. If the data are distorted, corresponding conclusions may be incorrect. We demonstrate how Benford's law, the distribution that first digits of numbers in certain data sets should follow, can be used to test for data abnormalities. We conduct an analysis of nine commonly used data sets and find that much data from developing countries is of poor quality while data from the United States seems to be of better quality. Female and male respondents give data of similar quality. (Contains 10 tables and 10 footnotes.)