Better assessment of physical function: item improvement is neglected but essential

Abstract

IntroductionPhysical function is a key component of patient-reported outcome (PRO) assessment in rheumatology. Modern psychometric methods, such as Item Response Theory (IRT) and Computerized Adaptive Testing, can materially improve measurement precision at the item level. We present the qualitative and quantitative item-evaluation process for developing the Patient Reported Outcomes Measurement Information System (PROMIS) Physical Function item bank.MethodsThe process was stepwise: we searched extensively to identify extant Physical Function items and then classified and selectively reduced the item pool. We evaluated retained items for content, clarity, relevance and comprehension, reading level, and translation ease by experts and patient surveys, focus groups, and cognitive interviews. We then assessed items by using classic test theory and IRT, used confirmatory factor analyses to estimate item parameters, and graded response modeling for parameter estimation. We retained the 20 Legacy (original) Health Assessment Questionnaire Disability Index (HAQ-DI) and the 10 SF-36's PF-10 items for comparison. Subjects were from rheumatoid arthritis, osteoarthritis, and healthy aging cohorts (n = 1,100) and a national Internet sample of 21,133 subjects.ResultsWe identified 1,860 items. After qualitative and quantitative evaluation, 124 newly developed PROMIS items composed the PROMIS item bank, which included revised Legacy items with good fit that met IRT model assumptions. Results showed that the clearest and best-understood items were simple, in the present tense, and straightforward. Basic tasks (like dressing) were more relevant and important versus complex ones (like dancing). Revised HAQ-DI and PF-10 items with five response options had higher item-information content than did comparable original Legacy items with fewer response options. IRT analyses showed that the Physical Function domain satisfied general criteria for unidimensionality with one-, two-, three-, and four-factor models having comparable model fits. Correlations between factors in the test data sets were > 0.90.ConclusionsItem improvement must underlie attempts to improve outcome assessment. The clear, personally important and relevant, ability-framed items in the PROMIS Physical Function item bank perform well in PRO assessment. They will benefit from further study and application in a wider variety of rheumatic diseases in diverse clinical groups, including those at the extremes of physical functioning, and in different administration modes.

Establishing a Common Metric for Physical Function: Linking the HAQ-DI and SF-36 PF Subscale to PROMIS® Physical Function

“…The PROMIS PF item bank consists of 124 items that assess mobility (lower extremity), dexterity (upper extremity), axial or central (neck and back function), and complicated actions that cover multiple domains (e.g., daily living activities). 7,8,13 An example of an item is: BAre you able to carry a laundry basket up a flight of stairs?^The five response options range from BWithout any difficulty,^to BUnable to do.^The item bank can be administered in multiple ways. For example, there is a PROMIS PF 10-item short form with items selected to target the range of physical function with high levels of precision.…”

The PROMIS Physical Function Correlates With the QuickDASH in Patients With Upper Extremity Illness

“…The questions do not refer to a particular recall period, but involve the participant's status at the time of completion [7,21,35].…”

“…Initially, upper and lower extremity function was assessed together under PROMIS Physical Function because there was little distinction between upper and lower extremity conditions in initial field testing and validation [7,15,16]; an upper extremity-specific disability measure recently was released for PROMIS. We were surprised that the developers of the PROMIS Physical Function CAT found little difference when they separated upper and lower extremity questions.…”

Neighborhood disadvantage, individual-level socioeconomic position and physical function: A cross-sectional multilevel analysis

“…1 Difficulty with physical function, represented by the inability to perform usual activities of everyday life, is a serious problem among older persons. [2][3][4] The magnitude of this problem is likely to become substantially greater with continuing increases in longevity and in the size of the oldest population in most developed countries.…”