Development and assessment of floor and ceiling items for the PROMIS physical function item bank

INTRODUCTION: Disability and Physical Function (PF) outcome assessment has had limited ability to measure functional status at the floor (very poor functional abilities) or the ceiling (very high functional abilities). We sought to identify, develop and evaluate new floor and ceiling items to enable broader and more precise assessment of PF outcomes for the NIH Patient-Reported-Outcomes Measurement Information System (PROMIS). METHODS: We conducted two cross-sectional studies using NIH PROMIS item improvement protocols with expert review, participant survey and focus group methods. In Study 1, respondents with low PF abilities evaluated new floor items, and those with high PF abilities evaluated new ceiling items for clarity, importance and relevance. In Study 2, we compared difficulty ratings of new floor items by low functioning respondents and ceiling items by high functioning respondents to reference PROMIS PF-10 items. We used frequencies, percentages, means and standard deviations to analyze the data. RESULTS: In Study 1, low (n = 84) and high (n = 90) functioning respondents were mostly White, women, 70 years old, with some college, and disability scores of 0.62 and 0.30. More than 90% of the 31 new floor and 31 new ceiling items were rated as clear, important and relevant, leaving 26 ceiling and 30 floor items for Study 2. Low (n = 246) and high (n = 637) functioning Study 2 respondents were mostly White, women, 70 years old, with some college, and Health Assessment Questionnaire (HAQ) scores of 1.62 and 0.003. Compared to difficulty ratings of reference items, ceiling items were rated to be 10% more to greater than 40% more difficult to do, and floor items were rated to be about 12% to nearly 90% less difficult to do. CONCLUSIONS: These new floor and ceiling items considerably extend the measurable range of physical function at either extreme. They will help improve instrument performance in populations with broad functional ranges and those concentrated at one or the other extreme ends of functioning. Optimal use of these new items will be assisted by computerized adaptive testing (CAT), reducing questionnaire burden and insuring item administration to appropriate individuals.