The methodologic quality of randomization as assessed from reports of trials in specialist and general medical journals.

Objective: To assess the quality of randomization from reports of trials in a sample of specialist journals, and to compare those results with a similar assessment from a sample of general medical journals.

Design: Evaluation of all 206 reports of parallel-group randomized trials published in the 1990 and 1991 volumes of four journals of obstetrics and gynecology and of 81 reports of trials published during 1987 in four general medical journals.

Results: Of the reports published in the specialist and in the general medical journals, only 32% and 48%, respectively, reported having used an adequate method to generate random numbers; only 23% and 26%, respectively, contained information showing that steps had been taken to conceal assignment until the point of treatment allocation; and merely 9% and 15%, respectively, described adequate methods of both sequence generation and allocation concealment. In those reports of trials that had apparently used unrestricted randomization, the differences in sample sizes between treatment and control groups were much smaller than would be expected by chance, and that feature was more marked in the specialist journals. In reports of trials in which hypothesis tests had been used to compare baseline characteristics, only 2% of tests reported in specialist journals and 4% of tests reported in general journals were statistically significant, lower than the expected rate of 5%.

Conclusions: Generating unbiased comparison groups requires proper randomization, yet the reports in these specialist and general journals usually provided inadequate or unacceptable information. Additional analyses suggest that nonrandom manipulation of comparison groups and selective reporting of baseline comparisons may have occurred.