title: Rasch analysis of the International Wellbeing Index in older adults.
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.
authors.affiliation: National School of Public Health, Carlos III Institute of Health, Madrid, Spain. jforjaz@isciii.es
authors.forename: Maria João
authors.initials: MJ
authors.lastname: Forjaz
authors.forename: Alba
authors.initials: A
authors.lastname: Ayala
authors.forename: Carmen
authors.initials: C
authors.lastname: Rodriguez-Blazquez
authors.forename: Maria-Eugenia
authors.initials: ME
authors.lastname: Prieto-Flores
authors.forename: Gloria
authors.initials: G
authors.lastname: Fernandez-Mayoralas
authors.forename: Fermina
authors.initials: F
authors.lastname: Rojo-Perez
authors.forename: Pablo
authors.initials: P
authors.lastname: Martinez-Martin
mesh_terms: D000368:Aged; D005260:Female; D015577:Geriatric Assessment / Q000379:methods; D006801:Humans; D016014:Linear Models; D008297:Male; D008602:Mental Healing; D008875:Middle Aged; D011581:Psychological Tests / Q000592:standards*; D011594:Psychometrics; D015203:Reproducibility of Results; D012959:Socioeconomic Factors