The Reproducibility of a Visual Analogue Scale

The Visual Analogue Scale is a self-report tool that enables the patient to rate the severity of his (pain) complaints. A good reproducibility of the VAS is a prerequisite for its ability to detect clinically important changes over time. In our clinic, and on a routine basis, a VAS is used to evaluate changes over time in the patient-specific main complaints (Beurskens, AJHM et al., Pain. 1996; 65: 71) of Temporomandibular Disorder (TMD) patients. Objectives: To evaluate the reproducibility of the VAS-scores. At the initial visit, the TMD patients defined their main complaint and rated its severity on a VAS-scale. Methods: The left and right anchor words of the 100 mm scale were ‘no hindrance at all' and ‘most hindrance possible'. At their second visit and before the actual treatment started (2-4 weeks later), the patients rated the severity of their main complaint again on a VAS-scale and they also assessed important changes in their complaint on a five-point verbal scale (much worsened, slightly worsened, stable, slightly improved, much improved). Results: Thirty-three of the 56 TMD patients who have completed both VAS ratings so far, reported to be stable over time and their VAS-scores were used in this study. The Intraclass Correlation Coefficient between the first and second VAS-scores was 0.72. Despite this fair to good test-retest, the Smallest Detectable Difference ( Kropmans, ThJB et al., J Dent Res. 1999; 78: 784) in the individual VAS-scores was high: 36 mm. Conclusions: These preliminary results confirm that a good correlation between subsequent measurements does not necessarily indicate a good reproducibility. In a routine clinical setting the reproducibility of the VAS scores is rather low.