12 © American Dental Association Use keywords, indexing terms, and synonyms related to the components of the PICO question for the search. We suggest beginning with two PICO components as search terms rather than all four. Begin with search terms based on the population and intervention components of the PICO question, as the results will most likely include the comparison term or concept. Adding the outcome terms will further narrow the results, and these terms should be added if the initial search yields far too many results. Using all four components as search terms initially will narrow a search too early and will miss results that may be important. Use the Boolean operator OR to account for synonyms of the same concept. Conversely, use the Boolean operator AND to require different components to be present in the results. Refer to Figure 2 for examples of Boolean searching. Most databases have a thesaurus that lists the preferred terminology or subject headings used to index articles as they are added to the database. Searching by subject headings is a simple way to retrieve a smaller pool of relevant results, as subject headings standardize the search process and return results where the search term is considered a main topic (that is, subject) of the manuscript. When not using subject headings to search, limit the search to the title and abstract. If the initial search retrieves too many results, limit the results to secondary and preappraised literature such as clinical practice guidelines, summaries, critical summaries, and systematic reviews. If secondary literature does not exist, it will be necessary to consult primary studies we suggest initially limiting the search to randomized controlled trials as they are typically less prone to bias. Reference 1. Bastian H, Glasziou P, Chalmers I. “Seventy-five trials and eleven systematic reviews a day: how will we ever keep up?” PLoS medicine. 2010 7(9):e1000326. Most databases have a thesaurus that lists the preferred terminology or subject headings used to index articles as they are added to the database. Want to read the rest of chapter 2 and preview the entire book? Order the complete book at www.ADAcatalog.org.