The time-lagged dependent variable regarding alcohol consumption (lagged to the prior exam) eliminates serial correlation in the errors (28) (evaluated with a Lagrange multiplier test) and also substantially controls for principal's genetic endowment and any intrinsic, stable predilection to drink. Additionally, the lagged independent variable for a contact's drinking status substantially controls for homophily (25,29). The key variable of interest is a contact's alcohol consumption behavior at time t+1. A significant coefficient on this variable would suggest either that a contact's drinking affects a principal's drinking or that a principal and a contact experience contemporaneous events affecting both of their alcohol consumption behaviors. The possibility of omitted variables or unobserved events explaining the associations was tested by examining how the type or direction of the social relationship between principal and contact affected the association between principal and contact drinking.
