To the Editor: The case—control study by Perneger et al. (Dec. 22 issue)1 on the association of end-stage renal disease (ESRD) with analgesic drugs reaches inappropriate conclusions that are based on flawed methods. Fundamental to the validity of case—control studies is the requirement that the control population be similar to the case-patient population except for the case-defining characteristic.2 The authors compared predominantly black (54 percent) and male (58 percent) case patients with mainly nonblack (86 percent) and female (65 percent) control subjects. The adjustments made do not deal with the probable differences in the socioeconomic, educational, and residential (urban vs).
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