A little-known perspective on the I-squared statistic

The I-squared statistic has become hugely popular in meta-analysis. Motivated by the recent statement that 'Informally, it can be considered to reflect the extent to which confidence intervals displayed in a forest plot do not overlap with each other', this short note formalises this perspective. The insights provided by our analysis lend further weight to the interpretation of the I-squared statistic as a measure of inconsistency. This perspective reminds us that visual inspections of forest plots are vitally important when assessing between-study variation.