*Geek Box: Case-Control Study
Prospective cohort studies take a cohort of people from the population, and follow them prospectively, i.e., over time. The advantage to this design is that exposures – like diet, smoking, etc. – can be assessed before a disease develops in the participants, and this reduces the potential for recall bias. Another advantage of prospective cohort studies is the potential sample size, which can range into the thousands to hundreds of thousands of participants.
However, this comes with a potential disadvantage in terms of gathering more granular detail regarding exposures and participant characteristics, which would be prohibitively expensive to do with a cohort of, for example, >100,000 people. To navigate this potential hurdle, some additional study designs have been used, in particular case-control study designs.
In a case-control design, several healthy participants are selected as controls for each case of an outcome, e.g., each case of a disease that has diagnosed. In this design, the researchers identify cases of their outcome of interest – we’ll stick with breast cancer as our example – that have already occurred, or as they occur if the parent study is a prospective cohort, and then select up to 4 to 5 healthy controls to match with a case of BC.
Ideally, they will seek controls who have a similar risk profile to the cases of BC, only the controls do not have the diagnoses itself. For example, if premenopausal BC was the outcome of interest, the researchers would want to have the controls also be premenopausal women. The case-control study would then compare, for example, dietary intake or estrogen-receptor status in the healthy controls vs. the BC cases.
While case-control studies have some advantages, they can face some logistical hurdles, in particular if more than one disease outcome is of interest – which is common in prospective cohort studies – then it can be highly inefficient, as each case of each different disease would require its own set of healthy controls to be matched with. In addition, they require careful statistical analysis and adjustment for relevant confounders to make the comparison between cases and controls as equivocal as possible. However, case-control designs have the advantage of lower cost and more efficiency in execution, particularly where the outcome of interest is a single disease endpoint.