Improved responsiveness and reduced sample size requirements of PROMIS physical function scales with item response theory

Abstract

IntroductionThe Health Assessment Questionnaire Disability Index (HAQ) and the SF-36 PF-10, among other instruments, yield sensitive and valid Disability (Physical Function) endpoints. Modern techniques, such as Item Response Theory (IRT), now enable development of more precise instruments using improved items. The NIH Patient Reported Outcomes Measurement Information System (PROMIS) is charged with developing improved IRT-based tools. We compared the ability to detect change in physical function using original (Legacy) instruments with Item-Improved and PROMIS IRT-based instruments.MethodsWe studied two Legacy (original) Physical Function/Disability instruments (HAQ, PF-10), their item-improved derivatives (Item-Improved HAQ and PF-10), and the IRT-based PROMIS Physical Function 10- (PROMIS PF 10) and 20-item (PROMIS PF 20) instruments. We compared sensitivity to detect 12-month changes in physical function in 451 rheumatoid arthritis (RA) patients and assessed relative responsiveness using P-values, effect sizes (ES), and sample size requirements.ResultsThe study sample was 81% female, 87% Caucasian, 65 years of age, had 14 years of education, and had moderate baseline disability. All instruments were sensitive to detecting change (< 0.05) in physical function over one year. The most responsive instruments in these patients were the Item-Improved HAQ and the PROMIS PF 20. IRT-improved instruments could detect a 1.2% difference with 80% power, while reference instruments could detect only a 2.3% difference (P < 0.01). The best IRT-based instruments required only one-quarter of the sample sizes of the Legacy (PF-10) comparator (95 versus 427). The HAQ outperformed the PF-10 in more impaired populations; the reverse was true in more normal populations. Considering especially the range of severity measured, the PROMIS PF 20 appears the most responsive instrument.ConclusionsPhysical Function scales using item improved or IRT-based items can result in greater responsiveness and precision across a broader range of physical function. This can reduce sample size requirements and thus study costs.

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

“…Recent draft recommendations from the Federal and Drug Administration (FDA) endorsed the HAQ-DI for use in drug trails of rheumatoid arthritis (RA) 12 . Nevertheless, recent studies have demonstrated the advantage of a ten-item CAT and 20-item short-form of the PROMIS PF instrument compared to the HAQ-DI in terms of measurement precision and range of coverage 8,10 . These results suggest that the PROMIS PF-20 can be used in place of the HAQ-DI in clinical trials, and still allow for the estimation of HAQ-DI scores for comparison with earlier clinical trials.…”

“…The instruments have generally shown improved measurement precision over existing measures such as the HAQ-DI and the SF-36® PF, particularly for PROMIS PF CAT and in the moderate range of function. 8,10 In addition, the PROMIS metric uses the T-score (mean=50; standard deviation=10), which is centered on the US general population. 11 Thus, a PROMIS Physical Function T-score of 60 can be interpreted as being one standard deviation higher (better function) than the Baverage person^in the US.…”

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

“…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.…”

Factors Associated with Incomplete DASH Questionnaires

“…The questions are ranked so that once a patient reports difficulty with a specific task, difficulty with all more difficult tasks is assumed. IRT-based questionnaires can arrive at a patient's disability level with fewer questions [9,10,14,24]. Questions that are not relevant to the patient can be bypassed [14].…”