title: Changes in waiting-list patients over time: data on some commonly-used measures. Beware!
abstract: When samples of psychiatric patients are assessed on 2 occasions on state and trait measures, without any formal intervention having yet taken place, a mean change in scores towards less psychopathology is often observed. This re-test effect, which is a potential threat to the validity of longitudinal studies, has not been given serious attention by researchers using repeated administrations. The present study addressed this issue by examining re-test effects in 2 independent clinical samples with the Symptom Check List-90-Revised and other widely-used state and trait measures. Time intervals between intake and re-take were 3 months and 11-350 days (M = 93 days, median = 81 days). Results indicated that the re-test effect occurred for most of the measures. Where significant testing effects were observed, 54-72% of the patients had time 2 scores that were lower than the average time I scores. The importance and practical and scientific implications of the findings are discussed. Eleven hypotheses concerning the nature of the re-test effect are offered, including mood-congruent associative processing, natural coping mechanisms, self-monitoring hypothesis and response-shift.
authors.affiliation: Department of Clinical Psychology, University of Groningen, The Netherlands. w.arrindell@ppsw.rug.nl
authors.forename: W A
authors.initials: WA
authors.lastname: Arrindell
mesh_terms: D000328:Adult; D000368:Aged; D000379:Agoraphobia / Q000175:diagnosis* / Q000523:psychology / Q000628:therapy; D002986:Clinical Trials as Topic; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000175:diagnosis* / Q000523:psychology / Q000628:therapy; D008875:Middle Aged; D010043:Outcome and Process Assessment, Health Care; D016584:Panic Disorder / Q000175:diagnosis* / Q000523:psychology / Q000628:therapy; D010555:Personality Inventory / Q000706:statistics & numerical data*; D011594:Psychometrics; D015203:Reproducibility of Results; D014850:Waiting Lists