Aim: To analyze randomized controlled trials (RCTs) on pulmonary rehabilitation (PR) to determine whether the patients who complete PR form a representative subset of the chronic obstructive pulmonary disease (COPD) target population and to discuss what impact this may have for the generalizability and implementation of PR in practice.
Material and methods: A review of 26 RCTs included in a Cochrane Review 2007. We analyzed the selection at three different levels: 1) sampling; 2) inclusion and exclusion; 3) and dropout.
Results: Of 26 studies only 3 (12%) described the sampling as the number of patients contacted. In these studies 28% completed PR. In all we found, that 75% of the patients suitable for PR programs were omitted due to sampling exclusion and dropout. Most of the study populations are not representative of the target population.
Conclusion: The RCTs selected for the Cochrane review gave sparse information about the sampling procedure. The demand for high internal validity in studies on PR reduced their external validity. The patients completing PR programs in RCTs were not drawn from a representative subset of the target population. The ability to draw conclusions relevant to clinical practice from the results of the RCTs on PR is impaired.
Keywords: COPD; dropout; external validity; rehabilitation; selection.