Migration biases in address tracing by commercial firms

The results of a small experiment in address tracing have shown that subjects who were found by commercial tracing were less apt to have moved and were especially apt to have remained in the same state. The documented relation of migration and health status means that differential success in subject tracing can lead to subsequent study bias. Therefore, those who use commercial tracing of epidemiologic study subjects must carefully consider the possibility of a "missing migrant" effect, and that it may, in turn, produce a subsequent survey bias.