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How Many Patients? How Many Limbs? Analysis of Patients or Limbs in the Orthopaedic Literature: A Systematic Review

Bryant, Dianne MSc, PhD; Havey, Thomas C. BHSc; Roberts, Robin MSc; Guyatt, Gordon MD, MSc

Journal of Bone & Joint Surgery - American Volume: January 2006 - Volume 88 - Issue 1 - p 41–45
doi: 10.2106/JBJS.E.00272
Scientific Articles

Background: Clinical studies assessing orthopaedic interventions often include data from two limbs or multiple joints within single individuals. Without appropriate design or statistical approaches to address within-individual correlations, this practice may contribute to false precision and possible bias in estimates of treatment effect. We conducted a systematic review of the orthopaedic literature to determine the frequency of inappropriate inclusion of nonindependent limb or joint observations in clinical studies.

Methods: We identified seven orthopaedic journals with high Science Citation Index impact factors and retrieved all clinical studies for 2003 for any intervention on any limb or joint.

Results: We identified 288 clinical studies, 143 of which involved two limbs or multiple joint observations from single individuals. These studies included nineteen randomized clinical trials (13%) fifty-eight two-group cohort studies (41%), and sixty-six one-group cohort studies (46%). Seventy-six (53%) of the 143 studies involved statistical comparisons between patient groups with use of tests of association, and an additional sixty studies (42%) presented estimates of proportions without statistical comparisons. Only sixteen of the seventy-six studies involving statistical comparisons involved the use of any technique or methodological approach to account for multiple, nonindependent observations. A median of approximately 13% of the patients in these studies contributed more than one observation. The median proportion of nonindependent observations to total observations (the unit of analysis) was approximately 23%.

Conclusions: Our findings suggest that a high proportion (42%) of clinical studies in high-impact-factor orthopaedic journals involve the inappropriate use of multiple observations from single individuals, potentially biasing results. Orthopaedic researchers should attend to this issue when reporting results.

1 Faculty of Health Sciences, The University of Western Ontario, Elborn College Room 1438, London, ON N6G 1H1, Canada. E-mail address:

2 Michael G. DeGroote Centre for Learning and Discovery, Room 3308, Faculty of Health Sciences, McMaster University, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada

3 Clinical Epidemiology and Biostatistics, Faculty of Health Sciences, McMaster University, Hamilton Civic Hospital Research Centre, Henderson General Hospital, 711 Concession Street, Hamilton, ON L8V 1C3, Canada. E-mail address for R. Roberts:

4 Clinical Epidemiology and Biostatistics, Hamilton Health Sciences Center, Room 2C12, McMaster University, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada. E-mail address for G. Guyatt:

Copyright 2006 by The Journal of Bone and Joint Surgery, Incorporated
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