Measuring Up to Expectation: Cognitive Bias in Wrist Range-of-Motion Measurement.

Study Design Controlled laboratory study, cross-sectional design. Background The role of cognitive biases and their effect on a wide range of aspects relevant to clinical medicine has become the focus of a growing body of research, yet their effect in physical therapy is not well established. Objectives To test whether anchoring information provided to physical therapists prior to assessment of wrist range of motion (ROM) may induce bias in the measurement. Methods A total of 120 physical therapists participated in the study. Participants were asked to measure passive wrist extension ROM of a 65-year-old woman with no history of injury to the upper limb using a universal goniometer. Before initiating the measurement, some participants received a clinical description, which included sham information about the patient's health history. Three groups were differentiated according to the provided clinical content: no bias (n = 38), moderate bias (n = 41), and substantial bias (n = 41). An analysis of covariance was applied to test for differences between the 3 groups while controlling for any potential sex and experience effects. Results The analysis of covariance yielded a significant group effect (P = .009), with no significant effect for sex and experience. The adjusted mean wrist ROM was 80.2° for the no-bias group, 74.5° for the moderate-bias group, and 72.4° for the substantial-bias group. Post hoc tests demonstrated significant difference only between the group with no bias and the substantial-bias group (mean difference, 7.7°; P = .009). Conclusion Anchoring information was associated with differential results of an objective test. Physical therapists should increase their awareness of biases and consider employing debiasing strategies. J Orthop Sports Phys Ther 2016;46(12):1037-1041. Epub 30 Oct 2016. doi:10.2519/jospt.2016.6845.