Can we crowd-fund a meta-analysis? Simply find studies that report summary statistics, and add them to the dataset. The data so far: Study N r Willoughby (1927, 1928), A 90 0.44 Willoughby (1927, 1928), A 90 0.44 Jones (1928), A 105 0.60 Burks (1928), A 274 0.47 Colom et al 2002 342 0.492 Terman and Oden (1959), B unknown 0.481 Total N Weighted mean 901 0.488 Median 0.475