Duplicate publication bias weakens the validity of meta-analysis of immunosuppression after transplantation

Abstract

Duplicate publication can introduce significant bias into a meta-analysis if studies are inadvertently included more than once. Many studies are published in more than one journal to maximize readership and impact of the study findings. Inclusion of multiple publications of the same study within a meta-analysis affords inappropriate weight to the duplicated data if reports of the same study are not linked together. As studies which have positive findings are more likely to be published in multiple journals this leads to a potential overestimate of the benefits of an intervention. Recent advances in immunosuppression strategies following liver transplantation have led to many studies investigating immunosuppressive regimes including immunosuppression monotherapy. In this letter we focus on a recently published meta-analysis by Lan et al investigating studies assessing immunosuppression monotherapy for liver transplantation. The authors claim to have identified fourteen separate randomised studies investigating immunosuppression monotherapy. Seven of the references appear to relate to only three studies which have been subject to duplicate publication. Several similarities can be identified in each of the duplicate publications including similar authorship, identical immunosuppression regimes, identical dates of enrolment and citation of the original publication in the subsequent manuscripts. We discuss the evidence of the duplicate publication inclusion in the meta-analysis.

A systematic review and combined meta‐analysis of concentration of oral amisulpride

“…Given that all 3 studies comparing the concentrations between EPS‐groups and non‐EPS groups are from the same group, the sample sizes to some extent probably overlap. To avoid increasing the mean effect size and introducing significant bias , we have not pooled the result from the 3 studies . Regarding the relationship between concentration and clinical response, no significant difference in plasma levels between nonresponse and response groups was observed.…”

“…Original studies that met following criteria would be included in this study: (i) amisulpride plasma/serum concentration and either a dose, associated factors, clinical outcome, or side effect was also reported; and (ii) when 2 or more studies existed with an association to the same sample, the most recent study with the largest number was included. Exclusion criteria were: (i) studies with no accessible full text or conference paper; (ii) not in English or Chinese language; (iii) either the mean or standard deviation was not provided or not calculated; (iv) duplicate publications: identical samples and identical outcomes, identical samples and different outcomes, increased samples and identical outcomes, and decreased samples and identical outcomes …”

Assessment of Duplicate Publication of Chinese-Sponsored Randomized Clinical Trials

“…Aside from research integrity and legal considerations, the presence of duplicates carries the potential to distort evidence when an article may be counted more than once in systematic reviews. 3,4 Currently there is a gap between English and Chinese literature: most Chinese RCTs are published in Chinese and only indexed in Chinese bibliographic databases, and very few Chinese journals are covered by major English bibliographic databases. 14,16 At the same time, Englishlanguage systematic reviews, which should bridge the language gap, rarely search Chinese bibliographic databases and subsequently do not include RCTs published in Chinese.…”

Comparison of the efficacy and safety of phloroglucinol and magnesium sulfate in the treatment of threatened abortion

“…(3) Potential bias in systematic review [35–37] : Although we have thoroughly searched multiple Chinese and English databases to ensure precision and recall, it is impossible for us to completely rule out the possibility that some important documents might have been overlooked. In addition, the studies in all documents were performed in China, and we note that the documents included from Chinese databases have reported no negative results, indicating the possibility that publication bias exists.…”