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To the Editor: Although Dr Velicer and colleagues¹ controlled for confounding by indication for antibiotic use and the use of oral contraceptives, they apparently did not consider adjusting for comorbidity. There are several measures of comorbidity that the authors might have used.² The authors also did not consider the potential impact of use of nonsteroidal anti-inflammatory drugs (NSAIDs). While information about total NSAID use may not have been available from the database, use of prescription NSAIDs would be recorded. Although collected from a descriptive standpoint, other well-known factors associated with risk of breast cancer, such as ages at menarche and menopause, parity, family history of breast cancer, and body mass index, were not included in the analysis and could have affected the results.

While matching may improve efficiency, it can introduce a serious bias, especially when the matching variable is related to the exposure variable. In fact, matching may not . . . [Full Text of this Article]

Spencer E. Harpe, PharmD, MPH, PhD
harpe.3@osu.edu
College of Pharmacy
The Ohio State University
Columbus

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