The promise of PROMIS: using item response theory to improve assessment of patient-reported outcomes.

PROMIS (Patient-Reported-Outcomes Measurement Information System) is an NIH Roadmap network project intended to improve the reliability, validity, and precision of PROs and to provide definitive new instruments that will exceed the capabilities of classic instruments and enable improved outcome measurement for clinical research across all NIH institutes. Item response theory (IRT) measurement models now permit us to transition conventional health status assessment into an era of item banking and computerized adaptive testing (CAT). Item banking uses IRT measurement models and methods to develop item banks from large pools of items from many available questionnaires. IRT allows the reduction and improvement of items and assembles domains of items which are unidimensional and not excessively redundant. CAT provides a model-driven algorithm and software to iteratively select the most informative remaining item in a domain until a desired degree of precision is obtained. Through these approaches the number of patients required for a clinical trial may be reduced while holding statistical power constant. PROMIS tools, expected to improve precision and enable assessment at the individual patient level which should broaden the appeal of PROs, will begin to be available to the general medical community in 2008.