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
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.