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Attrition Bias in Rheumatoid Arthritis Databanks: A Case Study of 6346 Patients in 11 Databanks and 65,649 Administrations of the Health Assessment Questionnaire
ESWAR KRISHNAN, KIRSTEN MURTAGH, BONNIE BRUCE, DENISE CLINE, GURKIRPAL SINGH, and JAMES F. FRIES
ABSTRACT.
Methods. We studied the attrition patterns of patients with RA in 11 long-running databanks where patients were followed using semiannual Health Assessment Questionnaires. Attrition rates were calculated as the proportion of living patients who were in active followup at the cutoff date. Mantel-Haenszel methods and Weibull regression were used to model the relationship between attrition and age, sex, race, education, disease duration, functional disability, and other characteristics. Results. Overall, 6346 patients with RA were recruited into the study cohorts and followed for 32,823 person-years with 65,649 observations. The crude attrition rate was 3.8% per cycle. Rates were lowest in community-based databanks. Smaller size of the centers, inner-city location, and university clinic settings were associated with worse attrition. In multivariable analyses, younger age, lower levels of education, and non-Caucasian race predicted attrition. Level of disability and disease duration were not associated with attrition. Conclusion. In terms of person-years of followup and observation-points, this may be the largest study on attrition to date. While it is possible to have very high overall retention rates, certain types of databanks (smaller, inner-city-based, and university-based) are more likely to be biased due to selective retention of older, more educated Caucasian patients. (J Rheumatol 2004;31:1320-6) Key Indexing Terms:
PATIENT DROPOUTS
From the Division of Rheumatology, Department of Medicine, Stanford University, Palo Alto, California, and Clinical Research Center of Reading, West Reading, Pennsylvania, USA. Supported in part by grant AR43584 from the National Institutes of Health to ARAMIS (Arthritis, Rheumatism and Aging Medical Information System). E. Krishnan, MD, MPhil, Division of Rheumatology, Department of Medicine, Stanford University, and Clinical Research Center of Reading; K. Murtagh, MA; B. Bruce, DrPH; D. Cline, BA; G. Singh, MD; J.F. Fries, MD, Division of Rheumatology, Department of Medicine, Stanford Address reprint requests to Dr. E. Krishnan, Clinical Research Center of Reading, 401 Buttonwood Street, West Reading, PA 19611. E-mail: iyer@stanford.edu Submitted August 19, 2003; revision accepted January 29, 2004. |