The PROMIS of better outcome assessment: responsiveness, floor and ceiling effects, and Internet administration

Use of item response theory (IRT) and, subsequently, computerized adaptive testing (CAT), under the umbrella of the NIH-PROMIS initiative (National Institutes of Health-Patient-Reported Outcomes Measurement Information System), to bring strong new assets to the development of more sensitive, more widely applicable, and more efficiently administered patient-reported outcome (PRO) instruments. We present data on current progress in 3 crucial areas: floor and ceiling effects, responsiveness to change, and interactive computer-based administration over the Internet.

We examined nearly 1000 patients with rheumatoid arthritis and related diseases in a series of studies including a one-year longitudinal examination of detection of change; compared responsiveness of the Legacy SF-36 and HAQ-DI instruments with IRT-based instruments; performed a randomized head-to-head trial of 4 modes of item administration; and simulated the effect of lack of floor and ceiling items upon statistical power and sample sizes.

IRT-based PROMIS instruments are more sensitive to change, resulting in the potential to reduce sample size requirements substantially by up to a factor of 4. The modes of administration tested did not differ from each other in any instance by more than one-tenth of a standard deviation. Floor and ceiling effects greatly reduce the number of available subjects, particularly at the ceiling.

Failure to adequately address floor and ceiling effects, which determine the range of an instrument, can result in suboptimal assessment of many patients. Improved items, improved instruments, and computer-based administration improve PRO assessment and represent a fundamental advance in clinical outcomes research.