Recall bias in exposed subjects following a toxic exposure incident.

Attempts to reconstruct health effects following toxic exposure incidents may be subject to bias from distorted or incomplete recollection. We examined recall in 22 of 31 subjects exposed to fumes from ruptured drums containing nitric acid during a U.S. Environmental Protection Agency-supervised hazardous waste site clean up operation in August 1983. Exposed subjects were interviewed by emergency room staff immediately after the episode and the next morning by telephone by a public health epidemiologist. Six months later, the subjects were again interviewed by telephone and asked to report the symptoms they had experienced during the incident. For each respondent, symptoms recalled at 6 mo were compared to symptoms reported at the time. We found a low level of agreement compared to that expected by chance, associated with significant nonrandom differences in the distribution of responses consistently favoring selective recall on the later interview. We conclude that allowing time to elapse before obtaining data on individual symptoms following exposure may lead to a significant bias in response.