Accuracy and distribution of baseline categorical variables and -values in spine randomized controlled trials.

Levayer and colleagues assessed integrity issues in randomized controlled trials (RCTs) in four spine journals using baseline -values from categorical variables, concluding that there was no evidence of 'systemic fraudulent behaviour'. We used their published dataset to assess the accuracy of reported -values and whether observed and expected distributions of frequency counts and -values were consistent. In 51 out of 929 (5.5%) baseline variables, the sum of frequencies did not agree with the reported number of participants. For one-third of reported -values (172 out of 522), we could not calculate a matching -value using a range of statistical tests. Sparse data were common: for 22% (74 out of 332) of variables in which the reported -value matched the -value calculated from a chi-square test, the expected cells were smaller than recommended for the use of chi-square tests. There were 20-25% more two-arm trials with differences in frequency counts of 1 or 2 between-groups than expected. There were small differences between observed and expected distributions of baseline -values, but these depended on analysis methods. In summary, incorrectly reported -values and incorrect statistical test usage were common, and there were differences between observed and expected distributions of baseline -values and frequency counts, raising questions about the integrity of some RCTs in these journals.