The most important criterion that distinguishes and characterizes systemic reviews from other narrative reviews is being comprehensive . Thats why developing an explicit and comprehensive search strategy is considered a must and an indispensable step of systematic reviews, failure to attain such step through searching all available channels of information is a potential threat to the validity of the systematic review.
The information sources for systematic review comprise three main fold:
Academic bibliographic databases
Hand searching for printable journals, conferences and databases.
Informal channels for further data searching.
Limitations of quick searches:
Searching only one academic database suffers major shortcomings. First, that wont ensure retrieval of all relevant literature, according to previous study only 30-80 % of the available studies will be retrieved during searching a single database. Second, most databases tend to publish studies which shows effectiveness of interventions, not adverse effects. And finally databases like Medline for example English articles represent most of the indexed studies. To sum up searching a sole data bases will ends up with a systematic review that suffers selection bias, language bias and publication bias.[Suarez-Almazor, Belseck, Homik, Dorgan, &show more content
Considering its ease of use, simplicity and capability of obtaining a great number of relevant studies in a minimum time. Its worth noting that electronic searching should be pertained mainly to academic databases like PubMed and Cochrane central. The use of search engines like Google scholar, Intute and TRIP or publishers website as springer link and science direct should limited. Making a systematic review from articles obtained from such sources will surely suffer publication and selection bias.[Higgins & Green,