Choice of dose [in 196 double-blind trials of treatments for rheumatoid arthritis], multiple comparisons, wrong calculation, sub-group and within-group analyses, wrong sampling units. . . , change in measurement scales before analyses, baseline difference, and selecting reporting of significant results were some of the verified or possible causes for the large proportion of results that favored the [newly proposed] drug.
Doubtful or invalid statements were found in 76% of the conclusions or abstracts. Bias consistently favored the new drug in 81 trials, and the control in only one trial.
It is not obvious how a reliable meta-analysis could be done [reliably] in these trials.