Question

Given the discussion on the comparison between the population based design and the exposure-based design, we can compare the case-control design with the population-based design of the same sample size following the same logic. Please argue that

a) the most powerful choice of sample sizes in case-control study is n_D = n_D(bar) = n/2.

b)case-control study with equal sample sizes of cases and controls always leads to more powerful test than a population-based design of the same sample size

Answer 1

Given the discussion on the comparison between the population based design and the exposure-based design, we can compare the case-control design with the population-based design of the same sample size following the same logic.

a) Selection of controls is the most important point in case control studies. The way of control selection determines:  What is estimated (risk ratio, rate ratio, odds ratio) and the validity of estimate. Three basic tenets of comparability underlie attempts to minimize bias in control selection. These are the principles of study base, de-confounding, and comparable accuracy. Comparable accuracy principle. The degree of accuracy in measuring the exposure of interest for the cases should be equivalent to the degree of accuracy for the controls, unless the effect of the inaccuracy can be controlled in the analysis. Study base principle. Cases and controls should be "representative of the same base experience". De-confounding principle. Confounding should not be allowed to distort the estimation of effect. in this case if you have many cases you can select them systematically but it is better you select the new cases. selecting of control is important. you must first identify the source population that cases arise from it. If your study is a population-based case-control study, that uses a primary base. when ascertainment of all cases in a primary base is difficult or impractical, it may be preferable to use a secondary base. The base is defined as the source of the cases, and controls are individuals who would have become study cases if they had developed disease during the time of the investigation.

b) Because of the lack of power of case-control study designs to detect gene-environment interactions, flexible matching has recently been proposed as a method of improving efficiency. The power of a case-control study to detect interactions is low compared with the power to detect main effects. This has resulted in many different designs being proposed as strategies for improving power. In addition to matching strategies, because genetic risk factors are often under study, family designs have also been considered for studies of genegene or gene-environment interactions. that this method could offer a substantial improvement in statistical power. There are many scenarios in which environmental exposure, or at least a proxy thereof, may be measured in a relatively large set of potential controls.