OBJECTIVES This study explores the analytic implications of using questions about difficulty with daily activities that do not specify whether to consider assistance. METHODS For 1,054 Asset and Health Dynamics of the Oldest Old Study Wave 2 respondents, we compared responses to questions about difficulty without reference to assistance (ambiguous difficulty) to those about difficulty without...

The rst part of this paper provides rigorous deenitions for several basic concepts underlying the design of dependable programs, such as speciication, program semantics, exception, program correctness, robustness, failure, fault, and error. The second part investigates what it means to handle exceptions in modular programs structured as hierarchies of data abstractions. The problems to be solve...