In Reply.—The survey that Dr Jick is defending1 could have yielded a spurious association between reserpine use and breast cancer in women, if some uneven selection rates were taking place. The articles1.2 give no assurance that precautions were taken to prevent the Berkson fallacy. Let me illustrate how a spurious association could have occurred, and could have yielded the precise data reported by Dr Jick and his associates.
In describing the Boston Collaborative Drug Surveillance studies, the investigators stated2 that the survey patients were served in 24 hospitals that provided "about 45% of all general hospital beds in the greater metropolitan Boston area." They estimated that "approximately 1,300,000 people are served by these hospitals." The total population served might be estimated to be about 2.9 million. Half of these would be women: 1,450,000.
The incidence of breast cancer in women in the United States is about
BROWN GW. Berkson Fallacy and Studies on Reserpine and Breast Cancer-Reply. Am J Dis Child. 1976;130(10):1164–1165. doi:10.1001/archpedi.1976.02120110126027
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