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Daniel Goldman, MD, MPH
Austin, Tex

JAMA. 1997;277(11):883-884.

	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.

—In the articles on bicycle helmets and head injuries by Ms Thompson and colleagues,1,2 the authors state: "Our study design requires that both case and control groups have equal probability of striking their heads; that is, all cyclists must have experienced a crash." However, doesn't the probability of striking the head depend on crash circumstances? For example, while the authors believe it unlikely that there could be a 4-fold difference in risk-taking behavior between bicyclists, there could be at least a 4-fold difference in risk of head injury between riding slowly on a side street with little traffic vs, for example, riding at high speed in heavy traffic. General risk-taking behavior would also be important to consider. Furthermore, since cases were involved in more serious crashes than controls, the study does not have a comparable control group. To correct for this, the authors state they adjusted for "motor vehicle involvement." . . . [Full Text PDF of this Article]

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