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The simplest way to evaluate an intervention is to compare outcomes before and after implementation of the intervention. This method is known as an uncontrolled before-after study. The term ‘uncontrolled’ is used to distinguish this design from a controlled before-after study in which the before-after effect of implementation in the intervention group is compared with a control group that has no intervention. With the recent emphasis on improvements in healthcare delivery in particular, the number of uncontrolled before-after studies is increasing. Unfortunately, these present a problem.
The use of historical controls in clinical trials has long been recognised to overestimate the benefit of new treatments,1 and has provided misleading information in emergency medicine.2 ,3 For example, uncontrolled before-after data suggested that intravenous thrombolysis could reduce mortality in cardiac arrest,2 whereas subsequent randomised data showed that this treatment increased intracranial haemorrhage and did not reduce mortality.3 Emergency physicians would not generally consider basing their clinical practice on uncontrolled before-after data. …