Better measurement of the case-mix complexity of patients receiving rehabilitation services is critical to understanding variations in the outcomes achieved by patients treated in different postacute care (PAC) settings. The Medicare program recognized this issue and is undertaking a major initiative to develop a new patient-assessment instrument that would standardize case-mix measurement in inpatient rehabilitation facilities, long-term care hospitals, skilled nursing facilities, and home health agencies. The new instrument, called the Continuity Assessment Record and Evaluation Tool, builds on the scientific advances in measurement to develop standard measures of medical acuity, functional status, cognitive impairment, and social support related to resource need, outcomes, and continuity of care for use in all PAC settings.