Afentoula Mavrodi
University of Macedonia, Greece
Title: Reliability assessment of an instrument eliciting and interpreting willingness-to-pay values for quality of life improvement
Biography
Biography: Afentoula Mavrodi
Abstract
This study aimed at examining the test-retest reliability of an instrument developed to:
a) elicit a monetary value on a quality-adjusted life-year (QALY) using the Willingness-to-Pay (WTP) approach, within the Contingent Valuation Method (CVM); and b) capture general population’s motives regarding value assignment. Validation of this instrument constitutes part of a PhD research for which the candidate holds a scholarship from Onassis Foundation.
WTP was elicited in two ways (iterative closed-ended bidding system/open-ended question). Participants’ motives were assessed through 3 and 4 follow-up statements designed for those willing to pay for the hypothetical treatment and those not willing to pay (protest bidders), respectively.
The study was conducted in Thessaloniki, Greece, during October/November 2018. A randomly selected sample responded via telephone interviews on two occasions over a period of 4 weeks (n=97). Differences between the two points in time were evaluated using the Wilcoxon signed ranked test. Test-retest reliability was assessed using the intra-class correlation coefficient.
WTP estimates showed no statistically significant differences between the two points in time (p>0.05). Test-retest reliability was acceptable and very good for WTP and WTP per QALY estimates, respectively (ICC values of 0.67 (95% CI: 0.51, 0.78) and 0.85 (0.73, 0.91), respectively). Analysis revealed high reliability for all three motivation statements with coefficients ranging from 0.84 (0.67, 0.92) to 0.89 (0.89, 0.96). 3 out of 4 statements formulated exclusively for protest bidders showed acceptable/very good reliability (ICC values ranging from 0.84 (0.67, 0.92) to 0.89 (0.78, 0.95)). After excluding outliers, ICC for WTP estimates was improved at 0.93 (0.88, 0.96).