Fig. 1

Diagram representing four variables (columns) across different sample (rows). A standard cause (blue) is highly associated with the original outcome (yellow), and can be identified by most measures of association. However, a stratum cause (green) that only affects the outcome in a particular type of samples (\(1_A\)), could be missed from simple association with the outcome, and requires comparison against its corresponding outcome stratum (red) to be identified confidently