Internal validity refers to the extent to which the study’s conclusions are correct for which group?

• A. The general population beyond the study.
• B. The entire species under study.
• C. The sample of patients being studied.
• D. The study's statistical methods.

Answer: (B)

Internal validity is about whether the study’s conclusions about a causal relationship are correct for the participants actually studied, free from bias and confounding. Because it concerns the integrity of the study itself, the conclusions are best applied to the group that was studied—the study sample. If the study is well conducted, you can trust the treatment effect or association within that group of patients.

Generalizability to broader groups, like the general population beyond the study or the entire species, falls under external validity (how well findings extend beyond the studied sample). The study’s statistical methods are about how data are analyzed, not about which group the conclusions apply to.