Next, we performed causal simulations (with full genetic causality) to assess whether LCV is well-powered to detect a causal effect. We caution that LCV had lower power in simulations with LD (see below). First, we chose a set of default parameters: N=25k for each trait, 5% of SNPs causal for trait 1 (the causal trait), a (fully) causal effect of size q2 = 0.2 of trait 1 on trait 2, and 5% of SNPs causal for trait 2 only (Figure 3a). There were ~15 genome-wide significant SNPs on average, explaining ~2% of h2. LCV was well-powered to detect a causal effect at α = 0.001, while MR had lower power and bidirectional MR and MR-Egger had low power.
