Table 1. Empirical type- 1 error rates and power to detect an outlier study for M at threshold α = 0.05.

# Studies	# Variants	Type- 1 error	Power
30	50	0.050	98.9
	25	0.054	98.1
	10	0.056	39.9
15	50	0.033	99.2
	25	0.034	97.6
	10	0.039	40.3
10	50	0.024	98.7
	25	0.033	96.7
	10	0.025	35.7

GWAS meta-analysis simulation experiments each based on 1000 replicates. Studies were equally weighted (i.e. SE(β coefficients) = 0.08). Variant effect sizes for studies in the type-1 error analysis were sourced from an L-shaped distribution (S2 Table). In the power analysis, variant effect sizes for studies showing typical effects were sourced from S2 Table whilst effect sizes for variants in the outlier study were calculated as a multiple of the typical effect size. For example, effect sizes for variants in an outlier study 2-fold-stronger than studies showing typical effects would be computed as (2 x ({0.04, 0.12, 0.2, 0.28, 0.4}, σ = 0.10).