Health care in the United States is rapidly changing. In particular, two dramatic trends characterize this change: (1) the rise of the patient as a consumer and decision-maker and (2) the introduction of innovative technologies including a tremendous proliferation of both clinical and home diagnostic testing procedures (e.g., HIV testing, mammograms, prostate cancer tests, pap smears, genetic testing, pregnancy testing, sexually-transmitted disease tests, etc.). The proposed laboratory and survey research investigates how patients make these types of diagnostic testing decisions. Such an understanding of patient decision making should have important public policy implications. For instance, an understanding of the systematic decision making biases patients exhibit should allow for the development of interventions helping them to make better decisions. In making the decision as to whether or not to get tested, the patient has to decide what the value of the information is to him or to her in a rational, normative way. However, the potential life or death outcomes of medical decisions may generate negative emotion and stress and thus patients may react non-normatively to the provided information in order to cope. For example, normatively irrelevant, but emotionally salient, factors, such as testing errors, may influence one's perceived vulnerability to a disease. Patients' assessments of test information are expected to reflect this richer, emotionally perceived vulnerability rather than the more objective prior probability estimates that should be used to determine vulnerability. Investigation of three issues regarding diagnostic testing decisions will be conducted. First, research will investigate how patients interpret and use information regarding test accuracy; reactions to both test accuracy rates (i.e., overall false positive and false negative error rates for a particular test) and case information (i.e., the description of a particular false positive test result) will be considered. For instance, initial results indicate that a false positive result might inappropriately increase the patient's perceived vulnerability, and therefore subsequent test compliance, if the patient mis-attributes this erroneous test result to personal factors. Second, research will be conducted to identify what factors affect perceived vulnerability. Again, a particular focus will be on factors that are normatively irrelevant to one's prior probability of disease, but may influence the subjective value of test information. Finally, the research will assess patients' willingness to integrate both monetary and non-monetary costs across testing and treatment situations.