not immediately accepted. Eventually, however, the arguments for the inclusion of non-POW controls were persuasive: it would further strengthen the research by providing important comparison data to help interpret the findings among POWs. In sum, the combination of the VA's POW outreach program and the MFUA's research program was designed to produce a research survey with the best features of both kinds of programs.

Yet the opportunity to apply the existing mechanisms of the VA examination program to the MFUA cohort was not without its accompanying drawbacks. For example, although the widespread network of VA medical facilities provided coast-to-coast geographic coverage, it came with a built-in lack of standardization of examination procedures. Despite the publication of VA directives, the actual conduct of examinations necessarily varied from place to place and from time to time, in part as a result of local administrative customs, but mostly because of the underlying variability among examiners in the way they performed a "typical" examination. The study thus lacked the common, rigidly specified procedures of many research protocols. Yet despite these limitations, a large mass of important examination data has been accumulated.

DATA QUALITY

Before discussing the analysis of these data, some discussion of their quality is in order. The overall rate of completed, coded examinations, reported in Chapter 3, was disappointingly low—around 40–50% in POWs and 10–14% in controls. Some of the large difference in POW and control examination rates, in itself disquieting, is due to the fact that a number of POWs, the so-called volunteers, came in for examinations before the formal research program began. Because the VA's POW examination program began in 1983 and the research study began in 1986, there was ample opportunity for this to occur.

In general, however, at least in the previous morbidity follow-ups in 1967 (Beebe, 1975) and 1984 (Page, 1988), it has been the case that control response rates were lower than POW response rates. As evidence for this general statement, the same disparity in POW and control response rates is again seen in their responses to the supplemental psychological questionnaire mailing sponsored by the National Institute of Mental Health: questionnaire response rates were 25–30% for POWs and only 10–25% for controls. Interestingly, only relatively minor differences are apparent among POW groups or among control groups, except for the Korean conflict POWs and controls. These groups each had the highest response rates among POWs and controls.

Chapter 3 also included brief comparisons of demographic aspects and VA hospitalization rates for respondents and nonrespondents. There were



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