Reliability and validity of a self-administration version of DEMQOL-Proxy.
This study aimed to investigate the reliability and validity of a self-administered version of DEMQOL-Proxy, a disease-specific instrument that measures health-related quality of life in people with dementia.



The sample consisted of 173 informal carers of people with dementia, aged 29 to 89 years old. Carers were mostly female, White/White British and closely related to the patient. They completed DEMQOL-Proxy (self-administered), EQ-5D-3L (proxy reported about the person with dementia), EQ-5D-3L (self-reported about their own health) and the Zarit Burden Interview. Using well-established methods from classical test theory, we evaluated scale level acceptability, reliability and convergent, discriminant and known-groups validity of DEMQOL-Proxy.



DEMQOL-Proxy (self-administered) showed high acceptability (3.5% missing data and 0% scores at floor or ceiling), high internal consistency reliability (α = 0.93) and good convergent and discriminant validity. Amongst others, we found a moderately high correlation with EQ-5D-3L proxy reported (r = 0.52) and low to essentially zero correlations with EQ-5D-3L self-reported (r = 0.20) and carer and patient background variables (r ≤ 0.20). As predicted, DEMQOL-Proxy (self-administered) showed a modest correlation with DEMQOL (r = 0.32). Known-groups differences on health-related quality of life (comparing people with versus people without cognitive impairment) were of moderate effect size (d = 0.38) and in the expected direction.



DEMQOL-Proxy (self-administered) has comparable acceptability, reliability and validity with DEMQOL-Proxy (interviewer administered). DEMQOL-Proxy (self-administered) can be used in a wider variety of contexts than its interviewer-administered version, including routine use in busy clinics. Copyright © 2016 John Wiley & Sons, Ltd.
London School of Hygiene and Tropical Medicine, London, UK.
A A Jolijn
AAJ
Hendriks
London School of Hygiene and Tropical Medicine, London, UK.
Sarah C
SC
Smith
London School of Hygiene and Tropical Medicine, London, UK.
Theopisti
T
Chrysanthaki
London School of Hygiene and Tropical Medicine, London, UK.
Nick
N
Black
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017028:Caregivers; D060825:Cognitive Dysfunction; D003704:Dementia / Q000523:psychology*; D059026:Diagnostic Self Evaluation; D005006:Ethnicity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics / Q000295:instrumentation*; D011788:Quality of Life / Q000523:psychology; D015203:Reproducibility of Results; D057566:Self Report; D011795:Surveys and Questionnaires / Q000592:standards*
DEMQOL-Proxy; HRQL; dementia; psychometric properties; reliability; self-administration; validity