Evidence-appraisal glossary
I-squared
I-squared is the percentage of the total variation across studies in a meta-analysis that reflects genuine differences between studies rather than chance. Higher values mean the study results are more inconsistent with one another.
Also called: I2, I-squared statistic, Higgins I-squared.
Readers often use rough bands, with roughly 25, 50, and 75 percent taken as low, moderate, and high inconsistency. The key caveat is that I-squared is not an absolute measure of how far effects differ: it depends on how precise the included studies are, so a set of very large studies can push it high even when the actual differences are small, and it says nothing about the direction or clinical importance of those differences.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.