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Andrew N. Phillips, PhD
University College & Middlesex School of Medicine London, England

George Davey Smith, MD
University of Glasgow (Scotland)

JAMA. 1992;268(12):1539-1540.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

To the Editor.

—Halsey et al¹ reported an association between cigarette smoking and the risk of HIV-1 infection in Haitian women that remained after adjustment for "all known risk factors." The authors suggest two alternative explanations for their results: First, that there is a "hidden" or "unrecognized" confounder that has not been accounted for and, second, that there is a biologic effect of cigarette smoking on the risk of HIV transmission.

We would like to suggest a third possibility, namely, that the association is not due to an unknown confounder, but rather the inability to properly measure a well-known confounder—frequency of unprotected sexual intercourse with an HIV-infected man or men. The dichotomous variable "3 lifetime sexual partners" that was used in the study is only a poor proxy measure of this true confounder and thus considerably underestimates its association with risk of HIV infection.^2-4 The underestimation of the . . . [Full Text PDF of this Article]

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