The rising costs of health care and interest in the evaluation of health services and systems have sparked an increased need for technology assessment. A variety of available methods of assessment are described in the Institute of Medicine's book Assessing Medical Technologies (1). Although such methods as the randomized controlled trial (RCT) are widely accepted and used, obtaining information by such methods often takes a considerable amount of time, expense, and sophistication in study design. These costs suggest that a broader range of methods for collecting information about health care technologies should be considered. A vast resource of data collected on patients, ranging from a provider's practice records to national data sets, might be useful for technology assessment if it could be properly appraised.