Clinical studies/trials historical examples

However, differences between the care provided to patients in the trial and that provided to patients in this group may be due as much to secular trends in the provision of medical care as they are to the adoption of a study protocol. For example, length of stay in the United States has decreased since the early 1980s, due in part to the implementation of the Medicare Prospective Payment System. Thus, historical cohorts from earlier periods may have had longer lengths of stay as inpatients than is currently seen in clinical practice. These data may suggest a protocol-induced decrease in length of stay when one actually does not exist. 

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