ORIGINAL ARTICLES Evaluation of a preliminary physical function item bank supported the expected advantages of the Patient-Reported Outcomes Measurement Information System (PROMIS) M. Rose a,b, * , J.B. Bjorner a,b , J. Becker a,b , J.F. Fries c , J.E. Ware a,d a Health Assessment Lab and QualityMetric Incorporated, 275 Wyman Street, Suite 120, Waltham, MA 02451, USA b Department of Psychosomatic Medicine and Psychotherapy, University Medical Center, Hamburg-Eppendorf, Germany c Stanford University School of Medicine, Palo Alto, CA, USA d School of Medicine, Department of Medicine, Tufts University, Boston, MA, USA Accepted 6 June 2006 Abstract Objective: The Patient-Reported Outcomes Measurement Information System (PROMIS) was initiated to improve precision, reduce respondent burden, and enhance the comparability of health outcomes measures. We used item response theory (IRT) to construct and evaluate a preliminary item bank for physical function assuming four subdomains. Study Design and Setting: Data from seven samples (N 5 17,726) using 136 items from nine questionnaires were evaluated. A gen- eralized partial credit model was used to estimate item parameters, which were normed to a mean of 50 (SD 5 10) in the US population. Item bank properties were evaluated through Computerized Adaptive Test (CAT) simulations. Results: IRT requirements were fulfilled by 70 items covering activities of daily living, lower extremity, and central body functions. The original item context partly affected parameter stability. Items on upper body function, and need for aid or devices did not fit the IRT model. In simulations, a 10-item CAT eliminated floor and decreased ceiling effects, achieving a small standard error (!2.2) across scores from 20 to 50 (reliability O0.95 for a representative US sample). This precision was not achieved over a similar range by any comparable fixed length item sets. Conclusion: The methods of the PROMIS project are likely to substantially improve measures of physical function and to increase the efficiency of their administration using CAT. Ó 2008 Elsevier Inc. All rights reserved. Keywords: Item response theory; Computerized Adaptive Test; Physical function; Health status; Questionnaire 1. Introduction Over the past several decades, the use of patient-reported outcomes (PROs) in clinical studies has steadily increased in frequency, as has their importance in evaluating therapies and developing treatment plans. The plethora of outcomes tools available today allows for increasing specification of a range of domains related to health and well-being, but with two major limitations. First, health outcomes research has produced a number of well validated instruments [1], but the most precise and comprehensive questionnaires are rather lengthy and complex, leading to a level of respondent burden that ham- pers recruitment, limits the representativeness of the patient population being studied, and leads to substantial problems of missing data. This is particularly important if different constructs are measured. Thus, the most popular health profile instruments are relatively short questionnaires (e.g., SF-36 Ò Health Survey [2,3]), but even for the mea- surement of one specific domain, like physical function, brief questionnaires are mostly favored (e.g., Health Assessment Questionnaire [HAQ] [4]). These shorter ques- tionnaires represent a compromise in measurement preci- sion, range, and other desirable attributes in favor of practicality. The short forms are useful for measuring the health status of larger groups, but the precision loss is of greater concern when groups are rather small or scores are estimated for individual patients to guide clinical deci- sion making [5]. * Corresponding author. Health Assessment Lab and QualityMetric Incorporated, 275 Wyman Street, Suite 120, Waltham, MA 02451, Tel.: 781-890-5544. E-mail address: mrose@hal-health.org (M. Rose). 0895-4356/08/$ e see front matter Ó 2008 Elsevier Inc. All rights reserved. doi: 10.1016/j.jclinepi.2006.06.025 Journal of Clinical Epidemiology 61 (2008) 17e33