Читать книгу Evidence in Medicine - Iain K. Crombie - Страница 34

Trial registration ‘was introduced in an effort to reduce publication bias and raise the quality of clinical research’ [68]. Although registration is strongly recommended, a recent study showed that only 53% of trials had had done so [69]. An analysis of over 1,100 trials explored the factors associated with registration. Compared to registered studies, trials that are unregistered are more likely to be of lower methodological quality. For example, they are less likely to have a defined primary outcome (48% vs 88%), more likely to have not reported or inadequate allocation concealment (76% vs 55%), less likely to report whether or not blinded (32% vs 15%), and more likely not to report details of attrition (67% vs 29%) [70]. When adjusted for methodological weaknesses, the unregistered trials had a modest increase in the average effect size compared to the registered studies. Another study evaluated 322 trials, and also showed a similar modest effect on treatment effect estimates [71]. Unregistered trials may give biased estimates of treatment effect.