Which option correctly pairs a common study design with its key strength or limitation?

Which option correctly pairs a common study design with its key strength or limitation?

• A. Randomized controlled trial — strong internal validity; limitation — generalizability is always poor
• B. Cohort — temporal relationship; limitation — absence of any bias
• C. Case-control — efficient for rare outcomes; limitation — recall bias
• D. Cross-sectional — quick snapshot; temporality is established

Answer: (C)

Case-control studies are designed around efficiency for studying rare outcomes. By starting with individuals who already have the outcome (cases) and comparing them to those without it (controls), you can look back to see how past exposures differ between the groups without following large numbers over time. The key limitation is recall bias: since exposure information is often collected after the outcome has occurred, cases may remember or report past exposures differently than controls, which can distort the observed association. The other options don’t fit as cleanly. Randomized controlled trials do have strong internal validity, but generalizability is not inherently poor—it depends on how representative the participants and setting are. Cohort studies do establish a temporal relationship (exposure before outcome) but are not free from bias, including selection bias and attrition. Cross-sectional studies offer a quick snapshot but cannot establish temporality, since exposure and outcome are measured at the same time.

Case-control studies are designed around efficiency for studying rare outcomes. By starting with individuals who already have the outcome (cases) and comparing them to those without it (controls), you can look back to see how past exposures differ between the groups without following large numbers over time. The key limitation is recall bias: since exposure information is often collected after the outcome has occurred, cases may remember or report past exposures differently than controls, which can distort the observed association.

The other options don’t fit as cleanly. Randomized controlled trials do have strong internal validity, but generalizability is not inherently poor—it depends on how representative the participants and setting are. Cohort studies do establish a temporal relationship (exposure before outcome) but are not free from bias, including selection bias and attrition. Cross-sectional studies offer a quick snapshot but cannot establish temporality, since exposure and outcome are measured at the same time.