Nevertheless, we have taken additional steps to assure the quality of the participant identification process. This process included a comparison between the current (1994) data set and the 1986 data set, as well as comparisons with two other sources of participation information—a roster of CROSSROADS participants from the National Association of Atomic Veterans (NAAV) and a roster compiled from direct solicitation of information from veterans by MFUA.
By comparing the current participant data set to the 1986 version and seeking verification of participation for sampled individuals, we were able to estimate a crude false positive rate and better understand changes that have occurred in the participant cohort over time. We drew a sample of 50 participants from each of the following categories:
MFUA requested documentation from NTPR to verify the status of each of the selected individuals. We then categorized every putative participant as a verified participant, a verified nonparticipant, or a person whose participation could not be verified using written documentary sources. To get a false positive rate we then calculated the fraction of inappropriately classified participants in the matched and new-only samples.
Estimating the number of persons erroneously left out of the study was more difficult than verifying the participation of those whose names were already known to be on the participant list. To estimate the false negative rate—