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Table 2 Overview of results

From: A comparison of results of empirical studies of supplementary search techniques and recommendations in review methodology handbooks: a methodological review

Method Includes What is the method used for What the evidence says Implications of evidence Claimed advantages Claimed disadvantages Resource requirements
Contacting study authors 6 studies Identify: unpublished, or on-going studies, missing or incomplete data, completed but unpublished studies Expert in field to review includes Contact original investigators through study report contact details—mainly e-mail/telephone E-mail considered effective with better responses from institutional addresses Additional studies identified; additional study data provided No guarantee of additional or all relevant information identified Challenging and time consuming Less successful for older studies Additional resources needed (may need up to 3 contact attempts with authors)
Citation chasing 9 studies Identify: further studies, clusters or networks or studies Backward and forward citation chasing using 3 electronic citation databases Effectiveness of electronic citation methods unclear and suggest using all 3 databases Not limited by keywords or indexing as bibliographic database searching is Reliant on the currency, accuracy and completeness of the underlying citation network Citation chasing of 46 studies = 79 h or 40 studies = 5 days
Handsearching 12 studies Identify: studies or publications not routinely indexed in, or identified by, searches of bibliographic databases, including recently published studies Manual examination of the contents of topic relevant journals, conference proceedings and abstracts Use experts to develop list of journals to handsearch Unique study identification, increased sensitivity; identifying studies missed or not indexed in databases Studies still missed by handsearching; time and access to resources; low precision Range between 6 min and 1 h per journal
Searching trial registers 3 studies Identify: unpublished, recently completed or on-going trialsFind adaptations to trial protocols reported study outcomes Comprehensive list of registries to search Should be completed as complementary and not in isolation Unique study identification Search interfaces lag behind major databases None reported
Web searching 5 studies Identify: studies not indexed in bibliographic databases. Retrieving grey literature, study protocols and on-going studies Relevant websites and using search engines Use advanced search functions where possible Unique study identification, hints to on-going or recently completed studies Difficulties in transparent search, quality and quantity of searches returned 429 results in 21 h; google searching 7.9 h; targeted web searching 9-11 h