  Suppose we are interested in the mean of an outcome that is subject to
nonignorable nonresponse. This paper develops new semiparametric estimation
methods with instrumental variables which affect nonresponse, but not the
outcome. The proposed estimators remain consistent and asymptotically normal
even under partial model misspecifications for two variation independent
nuisance components. We evaluate the performance of the proposed estimators via
a simulation study, and apply them in adjusting for missing data induced by HIV
testing refusal in the evaluation of HIV seroprevalence in Mochudi, Botswana,
using interviewer experience as an instrumental variable.
