| Abstract
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Randomized clinical trials and prospective observational studies are quality epidemiological study designs for evaluating treatments and for studying the outcomes of an exposure. Patent attrition from these studies is a potential threat to their validity. If potential drop-outs can be identified early in a study, then researchers can design strategies specifically targeting such patients to at least minimize their attrition. This research was carried out on data from two clinical trials of cognitive behavioral interventions to identify factors associated with patient who dropped out prematurely. In the first study 719 patients, of acute coronary syndrome (ACS), admitted to one of the five participating mid-Michigan hospitals were recruited. Following discharge, patients were approached by telephone at one-month baseline (n=525), 3 months (n=440), and 8 months (n=388). Following baseline interview patients were randomized to either a standard treatment arm or to standard treatment plus a cognitive intervention arm. Attrition of patients, following baseline interview (failure to complete the next scheduled interview) was modeled using a Generalized Estimating Equation (GEE) model, on a data set with multiple records per patient. The second data set is a group of cancer patients undergoing chemotherapy, at one of the six different hospitals in Michigan, Indiana and Ohio. Two hundred and sixty three patients consented to participate. Data collection was done at baseline (n=235), 10 weeks (n=178), 20 weeks (n=139), and 32 weeks (n= 125). Attrition following baseline was modeled in the same manner as for the cardiac patients. Age of the patient, smoking habits, depression and abstinence from alcohol were found to have an association with attrition in cardiac patients. Whereas among cancer patients, cancer of lung, time spent in trial, depression and education were found to significantly influence attrition. Patient attrition from longitudinal studies is mostly a function of their mental heath, social activity and support. Non-conformation with the expected role of the patient given the intervention under study in the trial also influences patients' chances of dropping out prematurely.
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