We appreciate the letters from Drs Gibbons and Cooper and from Drs Resnick and Greenspan. In general, we consider both letters in support of the basic recommendations we have advanced, but there are specific points in each that are worthy of comment. First, the statement referenced by Drs Gibbons and Cooper should have cited not only reference 60 of our article,1 but reference 61 by Bloom and Soper2 as well. This latter article reports the 80% false-positive rate. Drs Gibbons and Cooper are correct that Shepard's study found a false-positive rate of 70% assuming a 5% prevalence. Other articles assuming similar prevalence rates cite even higher false-positive rates.3,4 Obviously, the values cited for positive predictive value or false-positive rates depend on the values assumed for prevalence, sensitivity, and specificity. Regardless of which numbers one uses, the basic point remains the same: that the prevalence is
Harris SS, Caspersen CJ, DeFriese GH, Estes EH. Counseling About Physical Activity-Reply. JAMA. 1989;262(24):3407. doi:10.1001/jama.1989.03430240040020
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