Clinimetrics corner: the many faces of selection bias

Selection bias, also known as susceptibility bias in an intervention study or spectrum bias in a diagnostic accuracy study, is present throughout clinically applicable evidence in various forms. Selection bias implies that the intervention or diagnostic test has been studied in a less representative sample population, which can lead to inflated overall effect sizes and/or inaccurate findings. Within the literature, there are over 40 forms of selection bias that can influence the external validity of results. Recognition of selection bias is essential in the translation of evidence into effective clinical practice. This clinimetrics corner outlines the major biases that readers encounter and discusses key examples regarding pertinent orthopedic and manual therapy literature.