Evidence-appraisal glossary
Cochran's Q test
Cochran's Q is a statistical test for heterogeneity in a meta-analysis, checking whether the spread among study results is larger than chance alone would produce. A small p-value suggests real differences between studies exist.
Also called: Q statistic, Cochran Q, chi-squared test for heterogeneity.
Q is the weighted sum of each study's squared deviation from the pooled estimate, and it is the quantity from which I-squared is calculated. It should not be read as a simple present-or-absent switch for heterogeneity: with few studies it has low power and can miss real differences, while with many large studies it can flag differences too small to matter clinically.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.