Background: comprehensive and well implemented searches are necessary to minimize the chance of publication bias and to generate reliable systematic review findings. Guidance documents exist to help reviewers perform systematic searches, but to our knowledge, no formal classification of all possible ways of identifying studies for inclusion in a systematic review exists. This study aims to:
1) identify all possible methods used in systematic searching;
2) classify the methods into a hierarchical framework;
3) standardize the terminology used to describe the methods.
The framework will be used to review the evidence for each method in a future research project.
Objectives: to create a structured hierarchical framework of methods for the conduct of a systematic search of the literature.
Methods: we performed a systematic search of the literature and internet to identify documents or guides on conducting a systematic search to identify studies for inclusion in a systematic review. We identified methods of locating studies from these documents and web guides. We extracted these methods and categorized them into a structured hierarchical framework of methods. We then sought feedback from Cochrane Information Specialists to revise the framework.
Results: initially, we identified five documents from expert organizations. We conducted a search of the literature and internet which identified a further 4021 documents. After screening, we assessed 759 studies as potentially eligible, and extracted data from 72 of them. We sought feedback from Cochrane Information Specialists via email, and nine responded. Feedback was positive with minor modifications suggested. After incorporating search results and feedback, we created a final hierarchical framework of methods for conducting a systematic search.
The framework consists of four categories, each with multiple methods and element. Categories and the numbers of methods and elements are listed in their own table, they are:
1) selecting sources to search, contains three methods and 23 elements;
2) searching the literature electronically, contains seven methods and 74 elements;
3) other methods to identify relevant studies, contains four methods and 18 elements;
4) updating searches, contains two methods and 12 elements.
Conclusion: many methods exist for identifying studies for inclusion in systematic reviews. With the methods identified and classified, future work could focus on standardizing the terminology used, assessing the quality of the evidence for each method and then prioritizing research where it is needed.
Patient or healthcare consumer involvement: there was no direct patient or consumer involvement, although the ability to synthesize evidence on medical topics quickly will be of direct benefit to both these groups.