Baseline data in clinical trials

Although reporting baseline data seems simple, it is crucial information for readers in judging the validity of a trial. Knowing the baseline characteristics of the trial participants allows readers to assess how closely these match patients seen in their own clinical practice, and therefore how generalisable the results of the trial will be (so-called external validity). Baseline characteristics also allow the success of randomisation to be assessed. In studies where important baseline factors appear well balanced, it is likely that any differences in outcome between the intervention and control groups are a real effect of treatment (one component of internal validity). For these reasons, the reporting of baseline demographic and clinical characteristics of each group is a requirement of the CONSORT statement.1 The item and its descriptor as they appear in the CONSORT checklist are shown in Box 1, and a checklist for baseline data is provided in Box 2.