Presentation of continuous outcomes in randomised trials: an observational study.

OBJECTIVE: To characterise the percentage of available outcome data being presented in reports of randomised clinical trials with continuous outcome measures, thereby determining the potential for incomplete reporting bias. DESIGN: Descriptive cross sectional study. DATA SOURCES: A random sample of 200 randomised trials from issues of 20 medical journals in a variety of specialties during 2007-09. MAIN OUTCOME MEASURES: For each paper's best reported primary outcome, we calculated the fraction of data reported using explicit scoring rules. For example, a two arm trial with 100 patients per limb that reported 2 sample sizes, 2 means, and 2 standard deviations reported 6/200 data elements (1.5%), but if that paper included a scatterplot with 200 points it would score 200/200 (100%). We also assessed compliance with 2001 CONSORT items about the reporting of results. RESULTS: The median percentage of data reported for the best reported continuous outcome was 9% (interquartile range 3-26%) but only 3.5% (3-7%) when we adjusted studies to 100 patients per arm to control for varying study size; 17% of articles showed 100% of the data. Tables were the predominant means of presenting the most data (59% of articles), but papers that used figures reported a higher proportion of data. There was substantial heterogeneity among journals with respect to our primary outcome and CONSORT compliance. LIMITATIONS: We studied continuous outcomes of randomised trials in higher impact journals. Results may not apply to categorical outcomes, other study designs, or other journals. CONCLUSIONS: Trialists present only a small fraction of available data. This paucity of data may increase the potential for incomplete reporting bias, a failure to present all relevant information about a study's findings.