Methodological issues in examining measurement equivalence in patient reported outcomes measures : Methods overview to the two - part series , “ Measurement equivalence of the Patient

The purpose of this article is to introduce the methods used and challenges confronted by the authors of this two-part series of articles describing the results of analyses of measurement equivalence of the short form scales from the Patient Reported Outcomes Measurement Information System (PROMIS). Qualitative and quantitative approaches used to examine differential item functioning (DIF) are reviewed briefly. Qualitative methods focused on generation of DIF hypotheses. The basic quantitative approaches used all rely on a latent variable model, and examine parameters either derived directly from item response theory (IRT) or from structural equation models (SEM). A key methods focus of these articles is to describe state-of-the art approaches to examination of measurement equivalence in eight domains: physical health, pain, fatigue, sleep, depression, anxiety, cognition, and social function. These articles represent the first time that DIF has been examined systematically in the PROMIS short form measures, particularly among ethnically diverse groups. This is also the first set of analyses to examine the performance of PROMIS short forms in patients with cancer. 1 Correspondence concerning this article should be addressed to: Jeanne A. Teresi, Ed.D, Ph.D., Columbia University Stroud Center at New York State Psychiatric Institute, 1051 Riverside Drive, Box 42, Room 2714, New York, New York, 10032-3702, USA; email: [email protected]; [email protected] 2 Weill Cornell Medical College, Division of Geriatrics and Palliative Medicine 3 Research Division, Hebrew Home at Riverdale; RiverSpring Health 4 Department of Psychiatry and Human Behavior, Department of Neurology, Warren Alpert Medical School, Brown University J. A. Teresi & R. N. Jones 38 Latent variable model state-of-the-art methods for examining measurement equivalence are introduced briefly in this paper to orient readers to the approaches adopted in this set of papers. Several methodological challenges underlying (DIF-free) anchor item selection and model assumption violations are presented as a backdrop for the articles in this two-part series on measurement equivalence of PROMIS measures.