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Rasch analysis of the International Wellbeing Index in older adults

Published online by Cambridge University Press:  16 August 2011

Maria João Forjaz*
Affiliation:
National School of Public Health, Carlos III Institute of Health, Madrid, Spain CIBERNED, Carlos III Institute of Health, Madrid, Spain
Alba Ayala
Affiliation:
National School of Public Health, Carlos III Institute of Health, Madrid, Spain
Carmen Rodriguez-Blazquez
Affiliation:
CIBERNED, Carlos III Institute of Health, Madrid, Spain National Centre of Epidemiology, Carlos III Institute of Health, Madrid, Spain
Maria-Eugenia Prieto-Flores
Affiliation:
National School of Public Health, Carlos III Institute of Health, Madrid, Spain
Gloria Fernandez-Mayoralas
Affiliation:
Center for Human and Social Sciences, Spanish National Research Council, Madrid, Spain
Fermina Rojo-Perez
Affiliation:
Center for Human and Social Sciences, Spanish National Research Council, Madrid, Spain
Pablo Martinez-Martin
Affiliation:
CIBERNED, Carlos III Institute of Health, Madrid, Spain Research Unit, Alzheimer Center Reina Sofia Foundation, Carlos III Institute of Health, Madrid, Spain
*
Correspondence should be addressed to: M.J. Forjaz, National School of Public Health, Carlos III Institute of Health, c/ Monforte de Lemos 5, 28029 Madrid, Spain. Phone: +34 91 822 2062; Fax: +34 91 387 7869/2. Email: [email protected].

Abstract

Background: The International Wellbeing Index is a measure of general quality of life formed by two scales: the Personal Wellbeing Index (PWI) and the National Wellbeing Index (NWI). This paper studies the psychometric properties of the PWI and NWI, using Rasch analysis and classic psychometric methods.

Methods: The PWI and NWI were applied to a representative sample of 1106 community-dwelling adults, aged 60 years and over, residing in Spain. Mean ± standard deviation age was 72.07 ± 7.83 years and 56.3% were women.

Results: Five PWI items (achieving in life, relationships, safety, community connectedness, and future security), and five NWI items (economic situation, state of environment, social conditions, business, and national security of the country) fitted the Rasch model. After adjusting the response scale format, satisfactory fit was obtained, with good reliability (person separation index of 0.91 for both the PSI and NWI), local independency of items, and strict unidimensionality. The measures showed adequate external construct validity with related measures.

Conclusions: The PWI and the NWI, with fewer items and simpler response scale formats, provided valid and reliable linear measures in older adults, according to Rasch and classic psychometric analyses.

Type
Research Article
Copyright
Copyright © International Psychogeriatric Association 2011

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