title: Applying the Expectancy-Value Model to understand health values.
abstract: OBJECTIVE
  Expectancy-Value Model (EVM) is the most structured model in psychology to predict attitudes by measuring attitudinal attributes (AAs) and relevant external variables. Because health value could be categorized as attitude, we aimed to apply EVM to explore its usefulness in explaining variances in health values and investigate underlying factors.
  
  
  METHODS
  Focus group discussion was carried out to identify the most common and significant AAs toward 5 different health states (coded as 11111, 11121, 21221, 32323, and 33333 in EuroQol Five-Dimension (EQ-5D) descriptive system). AAs were measured in a sum of multiplications of subjective probability (expectancy) and perceived value of attributes with 7-point Likert scales. Health values were measured using visual analog scales (VAS, range 0-1). External variables (age, sex, ethnicity, education, housing, marital status, and concurrent chronic diseases) were also incorporated into survey questionnaire distributed by convenience sampling among eligible respondents. Univariate analyses were used to identify external variables causing significant differences in VAS. Multiple linear regression model (MLR) and hierarchical regression model were used to investigate the explanatory power of AAs and possible significant external variable(s) separately or in combination, for each individual health state and a mixed scenario of five states, respectively.
  
  
  RESULTS
  Four AAs were identified, namely, "worsening your quality of life in terms of health" (WQoL), "adding a burden to your family" (BTF), "making you less independent" (MLI) and "unable to work or study" (UWS). Data were analyzed based on 232 respondents (mean [SD] age: 27.7 [15.07] years, 49.1% female). Health values varied significantly across 5 health states, ranging from 0.12 (33333) to 0.97 (11111). With no significant external variables identified, EVM explained up to 62% of the variances in health values across 5 health states. The explanatory power of 4 AAs were found to be between 13% and 28% in separate MLR models (P < 0.05). When data were analyzed for each health state, variances in health values became small and explanatory power of EVM was reduced to a range between 8% and 23%.
  
  
  CONCLUSIONS
  EVM was useful in explaining variances of health values and predicting important factors. Its power to explain small variances might be restricted due to limitations of 7-point Likert scale to measure AAs accurately. With further improvement and validation of a compatible continuous scale for more accurate measurement, EVM is expected to explain health values to a larger extent.
authors.affiliation: Department of Pharmacy, National University of Singapore, Singapore.
authors.forename: Xu-Hao
authors.initials: XH
authors.lastname: Zhang
authors.forename: Feng
authors.initials: F
authors.lastname: Xie
authors.forename: Hwee-Lin
authors.initials: HL
authors.lastname: Wee
authors.forename: Julian
authors.initials: J
authors.lastname: Thumboo
authors.forename: Shu-Chuen
authors.initials: SC
authors.lastname: Li
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001294:Attitude to Health; D005260:Female; D017144:Focus Groups; D006302:Health Services Research; D006305:Health Status Indicators; D006801:Humans; D007407:Interviews as Topic; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D012846:Singapore; D011795:Surveys and Questionnaires; D026712:Value of Life