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To the Editor: In their prospective study, Dr Leitzmann and colleagues¹ replicated the findings of our case-control study² in regard to a protective relationship between frequency of ejaculation and risk of prostate cancer. Although the study of Leitzmann et al avoids the potential for recall bias, for both their study and ours the accuracy of ejaculation assessment was likely to be affected by problems in recall of past practice, particularly of that in early adult life. We believe that the effect of such a bias would tend to be conservative and would have thus underestimated any real effect for ejaculation.

We were puzzled by the authors' choice of men with the second lowest frequency of ejaculation as the reference category. It would be interesting to see the relative risks produced by an analysis that combined the first 2 groups together as the reference category.

Unlike many other studies, we found . . . [Full Text of this Article]

Graham G. Giles, PhD
graham.giles@cancervic.org.au

Gianluca Severi, PhD; Dallas R. English, PhD
Cancer Epidemiology Centre
Cancer Council Victoria
Carlton Victoria, Australia

John L. Hopper, PhD
Centre for Genetic Epidemiology
University of Melbourne
Melbourne, Australia

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