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Article
December 22, 1989

Counseling About Physical Activity-Reply

Author Affiliations

UCLA School of Medicine Los Angeles, Calif
Centers for Disease Control Atlanta, Ga
University of North Carolina School of Medicine Chapel Hill
Duke University Medical Center Durham, NC

UCLA School of Medicine Los Angeles, Calif
Centers for Disease Control Atlanta, Ga
University of North Carolina School of Medicine Chapel Hill
Duke University Medical Center Durham, NC

JAMA. 1989;262(24):3407. doi:10.1001/jama.1989.03430240040020
Abstract

In Reply.—  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

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