An empirical study of the use of living versus deceased study subjects: Associations with liver cancer in the selected cancers study

PURPOSE: In case-control studies, the issue of whether living or deceased controls should be used for deceased cases has been controversial. METHODS: Using data from a study of cancer among men that selected both live (n = 1910) and deceased controls (n = 596) for cases of liver cancer (109 deceased, 59 living), we examined the effects of using information from proxy respondents (cases and controls) and from live cases and controls on associations between liver cancer and known risk factors. Cases diagnosed between 1984 and 1988 were selected from eight population-based cancer registries. Live controls were recruited by random digit dialing, deceased controls from death certificate files. Controls were matched to cases on geographic area, year-of-birth, and race. RESULTS: Adjusted odds ratios (OR) calculated for deceased cases and controls, when compared to odds ratios for live cases and controls, were attenuated towards the null value for history of hepatitis (4.7 vs. 14.9), blood transfusions (1.1 vs. 7.8), and cirrhosis (9.3 vs. 51.1). When all cases and living controls were used, odds ratios did not differ substantially from those for living cases and controls except for cirrhosis (OR = 154.2). For smoking, the odds ratios were similar in all analyses. Adjustment for type of interview (self, proxy) did not eliminate differences between results for living and deceased subjects; significant interactions were found between type of interview and hepatitis, cirrhosis, and blood transfusions. CONCLUSIONS: Selection of live controls for deceased cases is recommended to decrease misclassification in measures of exposure.