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Suppose a researcher is interested in the effect of military service on earnings using an instrumental variables (IV) analysis. In the U.S., during the Vietnam war, there was a draft (i.e. mandatory military service for some people) in which priority for the draft was determined by a national lottery. Note that some draft-eligible men were exempted and non-eligible men volunteered for military service. Angrist (1990, AER) uses the Vietnam draft lottery as an instrument to estimate the effect of Vietnam military service on earnings. The first stage in the IV analysis is O The effect of draft lottery on earnings The effect of Vietnam military service on earnings O The effect of earnings on Vietnam military service O The effect of draft lottery on Vietnam military service