It’s here that a serious form of bias known as “literature search bias”, may occur. Since all studies on a similar topic will not be listed in just one computer database, it’s usually important to search multiple databases (for example, Medline, Embase, CINAHL, etc.) in order to minimize your chances of omitting studies that may meet your inclusion criteria. It’s also important to check the bibliographies of retrieved studies and review articles in order to identify other studies that may meet your inclusion criteria. Furthermore, if time and resources are available, one should hand search appropriate journals for studies. Finally, having one or more experts on the topic review your reference list helps ensure that few, if any, studies have been omitted.