Final answer:
A case-control study is the most suitable design for examining rare diseases, given its retrospective nature that compares affected individuals with controls based on past behaviors. This approach is more practical for rare conditions than randomized controlled trials or cohort studies.
Step-by-step explanation:
The best study design for examining rare diseases is c) case-control study. This type of observational study is particularly suited for diseases that are uncommon because it is retrospective, meaning it compares subjects who have the disease (cases) to those who do not (controls), based on their past behaviors and exposures. Since rare diseases have a small number of cases, it's more practical and efficient to start with the cases and look back to determine exposure factors, rather than starting with a large group and waiting for a few cases to emerge as in cohort studies. Additionally, conducting a randomized controlled trial would not be feasible due to the rarity of the condition and difficulty in enlisting an adequate number of participants.
An example of a successful case-control study is the research conducted by Doll and Hill in 1950 on smoking and lung cancer. This classic case demonstrates how effective a case-control study can be in establishing associations between risk factors and diseases, even when the disease in question, like lung cancer at that time, was relatively less common compared to today.