Type I error by sample sizes, frequency of events and loop sample size. We assume equal number of trials per comparison (KAB = KAC = KBC = K = 1, …, 7) in the presence (τ2 ≠ 0) and absence (τ2 = 0) of heterogeneity. Circled points correspond to loops with K = 1 for which a fixed-effects model is employed. The region within the horizontal dotted lines defines the confidence interval for the 5% nominal level. IVDL: inverse variance method using the DerSimonian and Laird estimator, KHDL: Knapp-Hartung method with the DerSimonian and Laird estimator.