Fig 1. Liability exposure model with two periods of exposure.
L1 is the earlier liability, L2 is the later liability, G1 is a set of genetic variants associated with L1, G2 is a set of genetic variants associated with L2, G12 is a set of genetic variants associated with both L1 and L2. X1 is a measure of the exposure in the early time period X2 is a measure of the exposure at the second time period, Y is an outcome observed at one time only, U is a set of unobserved confounders of the exposure at each time period and the outcome. X1 and X2 are potentially measured with error, error in this measurement is uncorrelated with the genetic variants.