title: The response scale for the intellectual disability module of the WHOQOL: 5-point or 3-point?
abstract: OBJECTIVE
  To deal with the question of whether a 5-point response Likert scale should be changed to a 3-point scale when used in the field testing of people with intellectual disabilities (IDs), which was raised after the pilot study of World Health Organization Quality of Life (WHOQOL)-DIS, a module being developed with the World Health Organization measure of quality of life for disabilities.
  
  
  METHODS
  Three possible ways were used to generate hypothetical data by merging a 5-point scale into a 3-point scale. The analyses were based on both item response theory and classical measurement theory. The partial credit model for polytomous response was performed for item evaluation; the confirmatory factor analysis was used to check construct validity, the Cronbach's alpha for domain reliability, and correlation analyses for the relationship between the 5-point scale and the generated 3-point scale.
  
  
  RESULTS
  Most items with a 5-point response scale had disordered response options and/or unequal-length intervals between successive response options; these deficiencies were removed or improved without decline of validity and reliability in the hypothetical data of 3-point scales.
  
  
  CONCLUSIONS
  Instead of the 5-point scale, a 3-point scale could be used for IDs in the field test of developing the module WHOQOL-DIS.
authors: School of Public Health, Sun Yat-sen University, Guangzhou, China. fangjq@mail.sysu.edu.cn
authors: J
authors: J
authors: Fang
authors: M P
authors: MP
authors: Fleck
authors: A
authors: A
authors: Green
authors: K
authors: K
authors: McVilly
authors: Y
authors: Y
authors: Hao
authors: W
authors: W
authors: Tan
authors: R
authors: R
authors: Fu
authors: M
authors: M
authors: Power
mesh_terms: D000203:Activities of Daily Living / Q000145:classification; D000328:Adult; D002648:Child; D003431:Cross-Cultural Comparison; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007223:Infant; D008607:Intellectual Disability / Q000175:diagnosis* / Q000523:psychology; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011594:Psychometrics / Q000706:statistics & numerical data; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D014944:World Health Organization; D055815:Young Adult