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Directed acyclic graph (DAG) showing m single-nucleotide polymorphisms (SNPs) Gj used as instrumental variables for the association of exposure X with outcome Y in the presence of confounder U. Each SNP has an effect γj on X and a direct pleiotropic effect αj on Y. Under linear models for X and Y, the total effect of SNP j on Y is Γj = αj + βγj.
