Three plots illustrating Simpson's paradox in a meta-analysis of case-control studies: (a) Scatterplot of frequency of exposition (on a log odds scale) against proportion of cases (left panel). (b) Line plot displaying log odds ratios within studies (middle panel). 0 = control group, 1 = case group. (c) Curved overlay plot (right panel).
Rücker and Schumacher BMC Medical Research Methodology 2008 8:34 doi:10.1186/1471-2288-8-34