Evidence for social gradients in effects of all categories of intervention. A 'supermatrix' covering all categories of intervention consisting of six rows (one for each dimension of inequality) and three columns (one for each of the three competing hypotheses about the differential effects of each category of intervention). Each study is represented by a mark in each row for which that study had reported relevant results. Studies with 'hard' behavioural outcome measures are indicated with full-tone (black) bars, and studies with intermediate outcome measures with half-tone (grey) bars. The suitability of study design is indicated by the height of the bar. Each bar is annotated with the number of other methodological criteria (maximum six) met by that study. See Methods: Plotting the distribution of the evidence for further explanation.