the overlap rate of searching medical keywords in general search engines

background: knowing the rate of overlapping in results obtained from information retrieval tools is important to prevent waste of time. medical and health-related information has an outstanding place among the variety of information available on the internet. hence, this research aimed to study the rate of overlap among medical search results derived from mesh (medical subject headings) in general search engines. methods: this applied, descriptive, comparative approach survey was conducted in 2010. the research sample included 4 general search engines, i.e. yahoo, live search, google, and ask. in order to determine the rate of overlapping among the searches, 10 medical keywords were first selected randomly. the first 10 results retrieved by each search engine were then listed. finally, the overlap rate was calculated by means of microsoft excel. to determine the overlapping search results, 10 common terms were searched in the mentioned search engines. then, 10 results retrieved in the first page of each search engine were collected and compared. the overlap rate among the retrieved results was finally calculated using a checklist and a researcher-made equation whose validity was confirmed based on observations of the researchers, comments of some expert professors, and especially referring to related literature. in addition, due to the descriptive, comparative approach of the research, descriptive statistics revolving around a statistical equation was utilized.   results: it was found that search engines can retrieve 48% of relevant searches retrieved by other search engines. yahoo had the highest number of unique results while google had the highest number of results overlapping with other search engines. the overlap rate of the 4 studied search engines was 11%. conclusion: the results obtained from different search engines hardly overlap. therefore, users are suggested to search more than one search engine simultaneously to access more relevant documents. moreover, they are advised to use specialized search engines to search medical information.