FIGURE 1 | Flow chart for instrumental variable (IV) selection. The fl ow chart shows the selection process of insomnia IVs to estimate the causal effects on bipolar disorder (BD), major depression (MDD), and schizophrenia (SCZ). First, we use p < 5.00E-8 to select index single-nucleotide polymorphisms (SNPs) to ensure that they stronglyassociatewithinsomnia.Second,weuse r 2 > 0.001intherangeof10,000 MbtoselectindependentindexSNPs.WetreattheEURof1000GenomeProjectas the reference panel. The fi rst two steps are completed by PLINK. Finally, we obtain 13 IVs on BD, 10 IVs on MDD, and 13 IVs on SCZ.