Empirical researchers commonly use instrumental variable (IV) assumptions to identify treatment effects. However, the credibility of these assumptions are often questionable. This paper considers what can be learned when the assumptions necessary for point identification are violated in two...

Data on 2,822 Vanderbilt University graduates are used to investigate alumni giving behavior during the eight years after graduation. A two stage model accounting for incidental truncation is used to first estimate the likelihood of making a contribution and second estimate the average gift size...