[Duplicate publication a way of embellishing research results. Unethical misuse which threatens the validity of systematic reviews and meta-analysis].

Studies showing favourable results tend to be published more than once. This practice of duplicate publication is, however, dishonest and unethical on the part of scientists and pharmaceutical companies. Inclusion into a meta-analysis of the results from multiple papers derived from one and the same controlled study gives an inflated picture of the efficacy of the treatment. If manufacturers and researchers not only made all their study data public but also registered trials prospectively these pitfalls could be avoided.