Prevalence of AD among whites: a summary by levels of severity.

OBJECTIVE: To determine age- and sex-specific AD prevalence rates for whites using each of four severity-based definitions of a case: a person diagnosed as having at least questionable AD, one diagnosed as having at least mild AD, one diagnosed as having moderate or severe AD, and one diagnosed as having severe AD.
METHODS: Data from 21 studies of Europeans and North Americans were pooled.
RESULTS: Empirically, one study, from East Boston, is an outlier. Applied to the US population of 1996, the obtained estimates yield a prevalence of 1.7 to 1.9 million cases, depending on whether the outlier study is excluded or included.
CONCLUSIONS: With disease severity taken into account, estimates of AD prevalence from white populations are more consistent than is usually acknowledged. By including disease severity in the case definition, variations in reported rates are much reduced. The outlier status of the East Boston study appears to result from the use of a definition of AD that differs from that used in the other 20 studies. Alternative explanations of the discrepancy between these estimates and the common estimate of 4 million cases are discussed.