There are multiple reasons why you may see different results when searching iSearch Analytics compared to PubMed. Use the headings below to jump to different scenarios that may be relevant to your question. You can also visit our Tutorials to ensure you are searching correctly or contact us at NIH-OPA_Support@nih.gov if your search is not returning the results that you were expecting.
Publication types
Search fields
Data handling/stemming
Person searches
Source data and updates
Publication types
By default, PubMed expands queries on publication types to include more specific subsets. For example, "Clinical Trial" is a broad category that includes "Randomized Controlled Trial" in PubMed. This means that searching "clinical trial" [pt] in PubMed will automatically return both clinical trial and randomized controlled trial publications. In order to search for only clinical trial publications, PubMed users must specify not to expand the query by searching "clinical trial" [pt:noexp]. iSearch Analytics does not automatically include publication type subsets but rather returns publications tagged with the exact publication type used in the search.
Search fields
PubMed and iSearch Analytics also use different default search fields when keywords are typed into the search bar. Without adding field tags, such as publication type as described above, PubMed defaults to searching every field of a citation; learn about changing PubMed search fields. iSearch Analytics, in contrast, defaults to searching a subset of fields specific to each dataset. You can easily change these fields using the searchable fields options.
Data handling/stemming
Keywords may also be handled differently in PubMed and iSearch Analytics. By default, iSearch Analytics uses stemming to change search terms from their plural form to their singular form so a larger set of results can be returned. This means searching for “flies” also returns results where “fly” is mentioned in the record. PubMed also searches singular and plural forms of words using their automatic term mapping, in addition to synonyms. For example, if child rearing is entered in the search box, PubMed would search: "child rearing"[MeSH Terms] OR ("child"[All Fields] AND "rearing"[All Fields]) OR "child rearing"[All Fields].
Person searches
Based on the above differences in search functions, along with the fact that iSearch Analytics includes disambiguated people, person searches will inevitably return different results. Learn more about disambiguation and how to search people in Analytics.
Source data and updates
Lastly, the three iSearch Analytics datasets and PubMed each update their source data and citations at different times, which may cause different search results. Check data sources and update frequencies for the iSearch Analytics Literature dataset.