Thurstone scaling revealed systematic health-state valuation differences between patients with dementia and proxies.
BACKGROUND
Conventional techniques to measure health-related quality of life (HRQoL) in a single value or index are complex, require abstract reasoning skills, and are prone to biases (e.g., adaptation). A possible alternative that requires less cognitive demand is Thurstone scaling. The present explorative study investigates the feasibility and concurrent validity of using Thurstone scaling to elicit health-state values in patients with dementia and their proxies.


METHODS
The participants in the present study were 145 pairs, consisting of community-dwelling persons with dementia and their proxies. We administered the prototype of the dementia quality-of-life instrument (DQI), a dementia-specific HRQoL index instrument, to both patients and proxies. The patient's health state as defined by the DQI was placed randomly among nine other DQI health states and these were ranked from best to worst. These rankings were used for Thurstone scaling. After ranking, the health states were placed on a visual analogue scale (VAS).


RESULTS
Thurstone scaling had a completion rate of 37% for patients and 88% for proxies. Thurstone scaling showed a high correspondence with VAS values. In addition, we identified a trend that shows that patients value most of the evaluated health states systematically lower than proxies.


CONCLUSIONS
Thurstone scaling proved to be unfeasible for most patients, but feasible for proxies. Its concurrent validity was supported and new insights into patient-proxy discrepancies were discovered.
Department of Epidemiology, Biostatistics and HTA, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands. s.arons@ebh.umcn.nl
Alexander M M
AM
Arons
Paul F M
PF
Krabbe
Carla J M
CJ
Schölzel-Dorenbos
Gert Jan
GJ
van der Wilt
Marcel G M
MG
Olde Rikkert
D000368:Aged; D000369:Aged, 80 and over; D017028:Caregivers / Q000523:psychology; D003704:Dementia / Q000523:psychology*; D005190:Family / Q000523:psychology; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D012720:Severity of Illness Index