Purpose: To test the effect of anchoring and object symmetry on the accuracy of visual estimates of angles by physical therapists. Method: Sixty licensed physical therapists estimated eight angles in each of the following groups: anchored symmetrical, anchored non-symmetrical, non-anchored symmetrical, and non-anchored non-symmetrical. A two way analysis of variance (ANOVA) was used to assess error associated with symmetry of objects and anchoring of angles. Correlation coefficients were calculated to evaluate the association between total error and years of experience, and between error and frequency of estimation in clinical practice. Results: The total mean absolute error for all angles was 9.9 (plus or minus) 8.1 degrees with a range of 0 to 47 degrees. There was a main effect for both symmetry and anchoring and a fair relationship was found between error and years of experience. There was virtually no correlation between error and visual estimation frequency in clinical practice. Estimates of near-orthogonal angles had the smallest errors. Conclusion: These findings suggest that physical therapists are slightly better at estimating angles with one anchored side. They also suggest that angles formed by symmetrical objects are estimated more accurately than nonsymmestrical objects. Because of the magnitude of effects from anchoring and symmetry were small, they may not be clinically meaningful. These findings are consistent with the findings of others who also found errors to be smaller for near-orthogonal angles. They differ in that we found a statistically significant decrease in error for anchored angles, whereas others found no anchoring effect. It is recommended that clinicians limit their visual estimation of joint angles to near-orthogonal angles, practice to gain experience, and assess their visual estimation accuracy prior to using it in clinical practice.
