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Extending the Floor and the Ceiling for Assessment of Physical Function
Author(s) -
Fries James F.,
Lingala Bharathi,
Siemons Liseth,
Glas Cees A. W.,
Cella David,
Hussain Yusra N.,
Bruce Bonnie,
Krishnan Eswar
Publication year - 2014
Publication title -
arthritis and rheumatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.106
H-Index - 314
eISSN - 2326-5205
pISSN - 2326-5191
DOI - 10.1002/art.38342
Subject(s) - ceiling effect , ceiling (cloud) , sample size determination , observational study , population , sample (material) , computerized adaptive testing , item response theory , patient reported outcomes measurement information system , item bank , psychology , physical therapy , physical medicine and rehabilitation , medicine , statistics , psychometrics , mathematics , environmental health , engineering , clinical psychology , structural engineering , pathology , chromatography , chemistry , alternative medicine
Objective To improve the assessment of physical function by enhancing precision of physical function assessment as it pertains to subjects at extreme ends of the health continuum (i.e., subjects with extremely poor function [“floor”] or extremely good health [“ceiling”]). Methods Under the Patient‐Reported Outcomes Measurement Information System (PROMIS) (a National Institutes of Health initiative), we developed new items to assess floor and ceiling physical function in order to supplement the existing item bank. Using item response theory and standard PROMIS methodology, we developed 31 floor items and 31 ceiling items and administered the items during a 12‐month prospective, observational study of 737 subjects whose health status was at either extreme. Effect size was calculated and change over time was compared across anchor instruments and across items. Using the observed changes in scores, we back‐calculated sample size requirements for the new and comparison measures. Results We studied 444 subjects who had been diagnosed as having a chronic illness and/or were of old age and 293 generally fit subjects (including athletes in training). Item response theory analyses confirmed that the new floor and ceiling items outperformed reference items ( P < 0.001). The estimated post hoc sample size requirements were reduced by a factor of 2–4 for the floor population and a factor of 2 for the ceiling population. Conclusion Extending the range of items by which physical function is measured can substantially improve measurement quality, reduce sample size requirements, and improve research efficiency. The paradigm shift from assessing disability to assessing physical function focuses assessment on the entire spectrum of physical function, signals improvement in the conceptual base of outcome assessment, and may be transformative as medical goals more closely approach societal goals for health.