Usefulness of EQ-5D for evaluation of health-related quality of life in young adults with first-episode psychosis.
OBJECTIVE
To evaluate the psychometric properties of the EQ-5D and the usefulness of this instrument in psychiatric practice as a measure of health-related quality of life (HRQoL) in a sample of young adults with first-episode psychosis.


METHODS
The validity of individual questionnaire items is studied using an Item Response/Latent Trait Theory modeling approach. Sensitivity of response patterns on EQ-5D items to particular diagnostic subtypes of psychosis is investigated using a finite mixture modeling approach through latent class analysis. Finally, a structural equation modeling framework is used to study differential item functioning via a multigroup approach.


RESULTS
Results suggest that the data closely correspond to the Rasch Rating Scale Model, and therefore that EQ-5D latent scores are equal interval measures. Despite comprising relatively few items, the instrument yields reliable measures of HRQoL for group comparisons and cost-effectiveness evaluation, but EQ-5D score is too imprecise for the assessment of HRQoL for clinical purposes at the individual level. A significant relationship was found between EQ-5D responses and type of psychosis due to inclusion of item anxiety/depression in EQ-5D. Two items (anxiety/depression, functioning in usual activities) showed an ethnicity bias.


CONCLUSIONS
Psychometric evidence confirmed the EQ-5D to be a valid, interval measure that is scalable according to Rasch principles.
Department of Psychiatry, Addenbrookes Hospital, University of Cambridge, Box 189, Cambridge, CB2 0QQ, UK. js883@cam.ac.uk
J
J
Stochl
T
T
Croudace
J
J
Perez
M
M
Birchwood
H
H
Lester
M
M
Marshall
T
T
Amos
V
V
Sharma
D
D
Fowler
P B
PB
Jones
D000293:Adolescent; D000328:Adult; D003362:Cost-Benefit Analysis; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D017063:Outcome Assessment, Health Care; D011594:Psychometrics / Q000295:instrumentation*; D011618:Psychotic Disorders / Q000523:psychology*; D011788:Quality of Life; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires; D013997:Time Factors; D055815:Young Adult