When should a researcher consider using a case-control study? Select all that apply. When exposure data are expensive or difficult to obtain When the disease is well-understood When the disease has a long induction and latent period When the disease is common

A researcher should consider using a case-control study in the following situations:

1. When exposure data are expensive or difficult to obtain: Case-control studies are retrospective and thus rely on existing records and recall by participants for exposure information. This makes them less expensive and easier to conduct than other types of studies that require direct measurement of exposures.

2. When the disease has a long induction and latent period: Case-control studies are particularly useful for studying diseases with long latency periods (the time between exposure and disease onset) because they look backwards in time to assess exposure status. This would not be feasible in a cohort study, for example, which would require following participants for a long period of time.

The other two options are not typically reasons to use a case-control study:

• Even if a disease is well-understood, that doesn't necessarily mean a case-control study is the best choice. The choice of study design depends more on the specific research question, the nature of the exposure and outcome, and practical considerations.

• Case-control studies are usually not the best choice for studying common diseases. This is because with common diseases, it's harder to find a control group that's representative of the population without the disease. Cohort studies are usually better for studying common diseases.