title: Harmonizing Measures of Cognitive Performance Across International Surveys of Aging Using Item Response Theory.
abstract: OBJECTIVE
  To harmonize measures of cognitive performance using item response theory (IRT) across two international aging studies.
  
  
  METHODS
  Data for persons ≥65 years from the Health and Retirement Study (HRS, N = 9,471) and the English Longitudinal Study of Aging (ELSA, N = 5,444). Cognitive performance measures varied (HRS fielded 25, ELSA 13); 9 were in common. Measurement precision was examined for IRT scores based on (a) common items, (b) common items adjusted for differential item functioning (DIF), and (c) DIF-adjusted all items.
  
  
  RESULTS
  Three common items (day of date, immediate word recall, and delayed word recall) demonstrated DIF by survey. Adding survey-specific items improved precision but mainly for HRS respondents at lower cognitive levels.
  
  
  CONCLUSIONS
  IRT offers a feasible strategy for harmonizing cognitive performance measures across other surveys and for other multi-item constructs of interest in studies of aging. Practical implications depend on sample distribution and the difficulty mix of in-common and survey-specific items.
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA kchan10@jhu.edu.
authors.forename: Kitty S
authors.initials: KS
authors.lastname: Chan
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
authors.forename: Alden L
authors.initials: AL
authors.lastname: Gross
authors.affiliation: Medical College of Wisconsin, Milwaukee, USA.
authors.forename: Liliana E
authors.initials: LE
authors.lastname: Pezzin
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, MD, USA The Copper Ridge Institute, Sykesville, MD, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Brandt
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
authors.forename: Judith D
authors.initials: JD
authors.lastname: Kasper
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000523:psychology*; D003071:Cognition / Q000502:physiology*; D005260:Female; D006801:Humans; D038622:Internationality; D008137:Longitudinal Studies; D008297:Male; D011582:Psychological Theory; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D006113:United Kingdom; D014481:United States
keywords: cognitive performance; item response theory; surveys