Varying the item format improved the range of measurement in patient-reported outcome measures assessing physical function
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- Varying the item format improved the range of measurement in patient-reported outcome measures assessing physical function
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Gregor Liegl, Barbara Gandek, H. Felix Fischer, Jakob B. Bjorner, John E.. Ware Jr., Matthias Rose, James F. Fries, Sandra Nolte
Methods: Three five-item PF short forms were constructed from the Patient-Reported Outcomes Measurement Information System (PROMIS®) wave 1 data. All forms included the same physical activities but varied in item stem and response scale: format A (“Are you able to …”; “without any difficulty”/“unable to do”); format B (“Does your health now limit you …”; “not at all”/“cannot do”); format C (“How difficult is it for you to …”; “very easy”/“impossible”). Each short-form item was answered by 2217–2835 subjects. We evaluated unidimensionality and estimated a graded response model for the 15 short-form items and remaining 119 items of the PROMIS PF bank to compare item and test information for the short forms along the PF continuum. We then used simulated data for five groups with different PF levels to illustrate differences in scoring precision between the short forms using different item formats.
Results: Sufficient unidimensionality of all short-form items and the original PF item bank was supported. Compared to formats A and B, format C increased the range of reliable measurement by about 0.5 standard deviations on the positive side of the PF continuum of the sample, provided more item information, and was more useful in distinguishing known groups with above-average functioning.
Conclusions: Using an item format with an extended response scale is an efficient option to increase the measurement range of self-reported physical function without changing the content of the measure or affecting the latent construct of the instrument.
|Journal||Arthritis Research & Therapy|
|Number of pages||12|
|Publication status||Published - 21 Mar 2017|
- Physical function, Patient-reported outcomes, Ceiling effects, Measurement range, Item-response theory, Item information, Response scale, Item format
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