Which question is MOST relevant to appraising a study's internal validity?

• A. Were instruments properly calibrated and outcomes properly measured?
• B. Will the costs be the same for patients in other clinics?
• C. Are the study outcomes worth the time and effort?
• D. Will patients in other clinics have a similar outcome?

Answer: (A)

The main concept being tested here is internal validity—the extent to which a study’s results accurately reflect what happened within the study itself, without distortions from how data were collected or measured. When instruments are properly calibrated and outcomes are measured accurately and consistently, you minimize measurement bias and misclassification. This means the observed effects are more likely due to the factors being studied rather than errors in data collection. In turn, the study’s conclusions about cause and effect within that sample become more trustworthy.

Options that focus on costs in other clinics or whether the outcomes are worth the time address generalizability or practical value rather than the integrity of the data collected in the study. The idea of similar outcomes in other clinics also concerns external validity, not the study’s internal rigor.