Figure 4.

Ecological fallacy in meta-regression. Hypothetical relationships between age and treatment effect both within trials (represented by lines) and between trials (represented by dots). Upper: treatment effect is related to age within each trial, but is not related to the mean age across trials. Lower: relationship occurs across trials, but not within trials. Stat Med, How should meta-regression analyses be undertaken and interpreted?, Thompson SG, Higgins JP, Copyright^© 2002 John Wiley & Sons Limited. Reproduced with permission [24].