A physical therapist reviews a meta-analysis and identifies a quantitative measure of the difference between two groups. Which term is most consistent with this measure?

• A. P-value
• B. Minimal detectable difference
• C. Effect size
• D. Sampling error

Answer: (C)

The key idea is the magnitude of how much one group differs from another. In a meta-analysis, this is captured by the effect size, a standardized measure of the difference between groups that lets us combine results across different studies and scales. The actual number might be a mean difference on a common scale, a standardized mean difference (like Cohen’s d) when scales vary, or a ratio for binary outcomes. P-values show whether a difference is statistically unlikely to occur by chance, but they don’t indicate how big the difference is. Minimal detectable difference is about the smallest change a study can reliably detect given variability and sample size, not the observed magnitude across groups. Sampling error refers to random variation from sampling, not the effect size. So the term that best matches a quantitative measure of how large the difference is between two groups in a meta-analysis is the effect size.