Visual analogue scales: scale recalibration by patients with dementia and their proxies.

Background: Visual analogue scales (VAS) are often used to measure health-related quality of life (HRQoL). However, when such scales contain ambiguous anchors like "best imaginable health state," they produce answers that are difficult to interpret, as such anchors are interpreted differently by respondents of different age. This phenomenon that people's interpretation of subjective response scales changes in response to changing circumstances is known as scale recalibration. The current study attempts to investigate whether scale recalibration in a patient sample with cognitive limitations and proxies differs from the general population.

Methods: The participants in the current study were 151 pairs of community-dwelling patients with dementia and their proxies. They were administered three VASs with different upper anchors; (A) "best imaginable health state," (B) "best imaginable health state for someone your age," and (C) "best imaginable health state for a 25-year-old." From literature, we inferred a conceptual model for the general population that predicts the ordinal relationship of the VASs to be B ≥ A ≥ C. This rank order is tested by repeated measure ANOVA's in the aforementioned populations.

Results: VAS scores of patients with dementia were in line with the conceptual model. Proxy VAS scores for assessing patient HRQoL were not in line with the model: A > B > C. In addition, proxy VAS scores for assessing their own health were not in line with the model: A > B > C.

Conclusion: Patients with dementia use the VAS in a similar way to the general population. Proxies assessing either patients or themselves differ from the general population.