Methodologic issues in observational studies.

Assessment of orthopaedic treatments depends primarily on studies that analyze data abstracted from medical records or collected prospectively for research purposes. Because treatment in these studies is determined by the surgeon and the patient rather than controlled by the researcher, these studies are referred to as observational. Most orthopaedics research uses the observational study design because it is less expensive and more timely, includes more representative patients, and leaves medical decision-making under the control of the physician and the patient. Biases associated with observational studies are influenced greatly by study design, methods of data collection, and statistical analysis. All observational studies should report factors influencing relevance (characteristics of patients, treatments, and outcome measures), and factors that influence validity (methods to obtain information and patient risk factors that may differ between treatments). Improved standards for reporting observational studies will facilitate the interpretation of results and the comparison of studies with conflicting results.