Journal
JOURNAL OF INTELLECTUAL DISABILITY RESEARCH
Volume 55, Issue -, Pages 537-549Publisher
WILEY
DOI: 10.1111/j.1365-2788.2011.01401.x
Keywords
factor analysis; intellectual disabilities; item response theory; Likert scale; physical disabilities; WHOQOL
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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. Conclusion 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.
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