Andrea L. Cheville, M.D., Mayo Clinic Physical Medicine and Rehabilitation consultant, discusses Item Response Theory (IRT). Historically patients were given fixed-length tests with precisely worded questions, all of which had to be administered for the test to be valid. In contrast, IRT holds that each item offers information and may eliminate the need to ask less-informative questions. Computer Adapted Testing (CAT) uses computer-based algorithms to sequentially select the most informative question to efficiently estimate a patient's performance level. Patient-reported outcomes (PRO) are being increasingly integrated in the care of patients by asking them about their quality of life, mood, symptoms and functional abilities. PROs are extremely flexible and can be administered in person or via computer or mobile devices, which makes them inexpensive and convenient. Enhanced patient quality of life increasingly becomes the holy grail in modern health care. Caregivers want to deliver and payers want to purchase value. Function is among the principal determinants of quality of life. A key part of maintaining patients' functionality is determining when to administer rehabilitation services to both chronically and acutely ill patient populations. Computer-adaptive testing is an efficient way to monitor patients and determine the right time and type of rehabilitation that they need to remain functional.