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Phys Ther. 2008 Sep;88(9):1078-87. doi: 10.2522/ptj.20070327. Epub 2008 Aug 8.

Benchmarking physical therapy clinic performance: statistical methods to enhance internal validity when using observational data.

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Providence VA Medical Center, Department of Community Health, Brown University, 2 Stimson Ave, Providence, RI 02912, USA.


Many clinics and payers are beginning programs to collect and interpret outcomes related to quality of care and provider performance (ie, benchmarking).


assessment is commonly done using observational research designs, which makes it important for those involved in these endeavors to appreciate the underlying challenges and limitations of these designs. This perspective article discusses the advantages and limitations of using observational research to evaluate quality of care and provider performance in order to inform clinicians, researchers, administrators, and policy makers who want to use data to guide practice and policy or critically appraise observational studies and benchmarking efforts. Threats to internal validity, including potential confounding, patient selection bias, and missing data, are discussed along with statistical methods commonly used to address these limitations. An example is given from a recent study comparing physical therapy clinic performance in terms of patient outcomes and service utilization with and without the use of these methods. The authors demonstrate that crude differences in clinic outcomes and service utilization tend to be inflated compared with the differences that are statistically adjusted for selected threats to internal validity. The authors conclude that quality of care measurement and ranking procedures that do not use similar methods may produce findings that may be misleading.

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