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Sources to search

The searching for literature for a systematic review should be rigorous and comprehensive to find ALL information available on a particular topic. It is therefore important to widely and thoroughly search published and unpublished research. 

There are several types of sources that you can search, including; databases, grey literature, trials, and reference lists. You can also try hand searching.

As an HDR candidate, you will most likely only use databases for your systematic review, although confirm with your supervisor their expectations on which sources to search. 

Databases – It is important to search across a range of databases as no one database covers all the related literature. It is not acceptable to search just one database. The decision regarding which databases to search depends on the topic of the review. The database searches need to be comprehensive and reproducible. 

Grey Literature – This is not controlled by commercial publishers but rather is produced by organisations, governments, and industry. Grey literature is less likely to exhibit publication bias and so can provide balance. 

Trials – Many clinical trials are unpublished, so when appropriate it is important to include unpublished and ongoing studies to minimise bias. 

Hand searching – Not all trial reports are included in bibliographic databases, and trials may not be easily identified in database search results when accessing the titles and abstracts. Hand searching is a manual page-by-page examination of relevant journals and conference proceedings in order to identify published trials.

Reference lists – It can be fruitful to search the reference lists of relevant systematic reviews and meta-analyses, as well as other key identified studies. Using this search method would be done in the preliminary stages to help determine that search results did contain these papers. 


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