Table 2 Overview of results
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Contacting study authors | 6 studies | Identify: unpublished, or on-going studies, missing or incomplete data, completed but unpublished studies Expert in field to review includes | Contact original investigators through study report contact details—mainly e-mail/telephone | E-mail considered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 = 79Â h or 40 studies = 5Â 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 6Â min and 1Â 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Searching trial registers | 3 studies | Identify: unpublished, recently completed or on-going trialsFind adaptations to trial protocols reported study outcomes | Comprehensive list of registries to search | Should be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 21Â h; google searching 7.9Â h; targeted web searching 9-11Â h |