This chapter explores ways to diagnose the potential for nonignorable nonresponse to cause problems. Section 7.1 describes how to define the range of possible values of population values that are consistent with the observed data. These calculations require virtually no assumptions and are robust to nonignorable nonresponse; they are simple yet tend to be uninformative. Section 7.2 shows how to postulate possible levels of nonignorability and assess how results would change.