Find duplicates among the PubMed, EMBASE, and Cochrane Library Databases in systematic review

Abstract

Background: Finding duplicates is an important phase of systematic review. However, no consensus regarding the methods to find duplicates has been provided. This study aims to describe a pragmatic strategy of combining auto- and hand-searching duplicates in systematic review and to evaluate the prevalence and characteristics of duplicates.

Methods and findings: Literatures regarding portal vein thrombosis (PVT) and Budd-Chiari syndrome (BCS) were searched by the PubMed, EMBASE, and Cochrane library databases. Duplicates included one index paper and one or more redundant papers. They were divided into type-I (duplicates among different databases) and type-II (duplicate publications in different journals/issues) duplicates. For type-I duplicates, reference items were further compared between index and redundant papers. Of 10936 papers regarding PVT, 2399 and 1307 were identified as auto- and hand-searched duplicates, respectively. The prevalence of auto- and hand-searched redundant papers was 11.0% (1201/10936) and 6.1% (665/10936), respectively. They included 3431 type-I and 275 type-II duplicates. Of 11403 papers regarding BCS, 3275 and 2064 were identified as auto- and hand-searched duplicates, respectively. The prevalence of auto- and hand-searched redundant papers was 14.4% (1640/11403) and 9.1% (1039/11403), respectively. They included 5053 type-I and 286 type-II duplicates. Most of type-I duplicates were identified by auto-searching method (69.5%, 2385/3431 in PVT literatures; 64.6%, 3263/5053 in BCS literatures). Nearly all type-II duplicates were identified by hand-searching method (94.9%, 261/275 in PVT literatures; 95.8%, 274/286 in BCS literatures). Compared with those identified by auto-searching method, type-I duplicates identified by hand-searching method had a significantly higher prevalence of wrong items (47/2385 versus 498/1046, p<0.0001 in PVT literatures; 30/3263 versus 778/1790, p<0.0001 in BCS literatures). Most of wrong items originated from EMBASE database.

Conclusion: Given the inadequacy of a single strategy of auto-searching method, a combined strategy of auto- and hand-searching methods should be employed to find duplicates in systematic review.

Figure 1. Study flowchart of finding duplicates in the literatures regarding portal vein thrombosis (panel A) and Budd-Chiari syndrome (panel B).

Figure 2. Proportion of wrong information of auto-searched (panel A) and hand-searched (panel B) type I duplicates from the literatures regarding portal vein thrombosis and that of auto-searched (panel C) and hand-searched (panel D) type I duplicates from literatures regarding Budd-Chiari syndrome.

Figure 3. Simplified scheme to identify duplicates in systematic review.

The scheme includes the third main steps. First, all literatures retrieved from different databases are combined into one Endnote library. In this Endnote library, “Find Duplicates” preferences are defined on “Edit” menu. Thus, duplicates can be automatically searched by Endnote library. Subsequently, the review authors should check the accuracy and identify the type of duplicates. Finally, the redundant papers are excluded. Considering that a single strategy of auto-searching method was inadequate, additional search should be very necessary. Second, the remaining literatures are alphabetically ordered according to the first authors’ names in the Endnote library. If the first authors were the same between two or more articles, the review authors would further read the titles, journals’ names, volumes, issues, and pages. Subsequently, if these articles had the same titles, journals’ names, and issues, they would be attributed to the type I duplicates. Notably, the review authors should identify whether the difference between index and redundant papers was acceptable or not. On the other hand, if these had the same or similar titles but different journals or issues, the review authors would further read the abstracts and/or full-texts to judge whether or not they could be attributed to the type II duplicates. Third, the remaining literatures were also alphabetically ordered according to the titles in the Endnote library. If the titles were the same between two or more articles, the review authors would further read the journals’ names, volumes, issues, and pages. Subsequently, if these articles had the same journals’ names and issues, they would be attributed to type I duplicates. Notably, the review authors should identify whether the difference between index and redundant papers was acceptable or not. On the other hand, if these articles had the same or similar titles but different journals or issues, the review authors would further read the abstracts and/or full-texts to judge whether or not they could be attributed to the type II duplicates. Finally, review authors should check the accuracy.