b. The group of CHD cases and a group of those who do not have CHD frequency matched to the cases for tea metabolism biomarker.
In a case-control study, it is essential to match the comparison groups to minimize the potential confounding effects of variables that could influence the relationship between tea consumption and CHD risk. In this context, matching means selecting control subjects who are similar to the cases in certain characteristics that could be potential confounders. The goal is to ensure that any observed association between tea consumption and CHD risk is not solely due to differences in these confounding factors.
In option b, the researcher aims to match the group of individuals without CHD to the cases with CHD based on the tea metabolism biomarker. This means selecting individuals from the non-CHD group in a way that their distribution of tea metabolism biomarker levels is similar to that of the CHD cases. By doing this, the researcher can better isolate the effect of tea consumption on CHD risk.
Options c and d do not mention matching based on the tea metabolism biomarker, which is a crucial variable of interest in this study. Option c only matches for age, which helps control for the effect of age on CHD risk but does not specifically address the potential confounding effect of the tea metabolism biomarker. Option d involves a random sample of individuals who drink tea and those who do not drink tea, but again, it does not account for the potential influence of the tea metabolism biomarker on CHD risk. Therefore, option b is the most appropriate choice for this case-control study.