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Analysis of Selection Bias in a Case‐Control Study of Renal Adenocarcinoma

Crude estimation of the selection probability ratio (SPR), described previously, was extended to stratified and multivariateestimation and used to assess selection bias in a case-control study of renal adenocarcinoma. I t was shown that the directly pooledestimate of the SPR, using the same weights as the directly pooled estimate of the exposure odds ratio (OR) from the case-controlstudy (assuming the OR and SPR are common to all strata and data are abundant), can be multiplied with the OR to yield anadjusted OR that is free from selection bias. Medical records of 548 interviewed cases were compared with 640 noninterviewedcases, and interviews at 640 controls were compared with mailed questionnaires from 272 (60%) of the noninterviewed controls.Age-sex-adjusted point estimates of SPRs ranged from 0.65 to 1.4. Multivariate estimates from binomial regression ranged from0.34 to 2.0. Higher socioeconomic status and history of renal stones were predictors of participation by both cases and controls.Obesity in women, hypertension, and nonsmoking were predictors in cases only. Heart disease was associated with controlparticipation and case nonparticipation. This study cast doubt on the OR for obesity in women and hypertension in the