Last Updated : February 1, 2023
Many CADTH search filters are intended for use with Ovid multifile searching, which allows you to search multiple databases simultaneously. CADTH uses multifile searching for duplicate removal within the Ovid platform. In our process, search strategies are created within individual databases then combined into a single multifile search. CADTH multifile filters are then used to limit the search. The CADTH multifile filters incorporate subject headings from each database noted in the filter’s title, along with relevant keywords. We design our filters to prevent unwanted mapping of subject headings across databases.
The following is a more detailed description of the Ovid multifile searching process.
Note that you can limit search strategies to a specific database or databases by using the Ovid database code for that specific database segment.
First, prepare and save your searches for each database separately. Then open all the databases you want to search. This is what Ovid calls a multifile search. Run 1 of the searches, such as your Embase search:
Line 1. dogs.ti
Line 2. cats.ti
Line 3. exp Pig/
Line 4. rabbits.ab
Line 5. or/1-4
Line 6. 5 use oemezd
Line 6 will limit the results of this part of the search to the Embase database only (oemezd is the database code for the Embase segment 1974 to present)
Then run another of your individual database searches (e.g., MEDLINE) with all databases still open.
Line 7. dogs.ti,ab
Line 8. cats.hw
Line 9. exp Swine/
Line 10. rabbits.ti,ab,hw
Line 11. or/7-10
Line 12. 11 use medall
Line 12 will limit the results of this part of the search to the MEDLINE database, specifically to the segment called MEDLINE All (1946 to Daily Update) (medall is the database code).
Run any other searches from other databases in a similar fashion. Then use OR to combine your individual database results together (line 6 OR line 12 OR …)
You can now apply the CADTH multifile filter of your choice. Use AND to filter the combined results from all databases.
Remove duplicates using the Deduplicate function in Ovid (this function is not available for searches with more than 6,000 results). We recommend removing duplicates as the final step in your search, after all limits have been applied.
Example of multifile searching in Embase and MEDLINE
Ovid database codes can be difficult to find, so we have provided a list. For databases that are not listed, you may need to consult the Ovid guide for that particular database.
Selected Ovid database segment codes:
Ovid database guides (segment codes listed under the heading Segments and Years of Coverage):
Complete list of all Ovid database segment codes
CADTH multifile filters will run properly when searching multiple databases, but they may require modification when used in a single database. When doing multifile searches, all fields do not have to be in all databases to work properly; however, each field needs to be in all databases for it to work in a single database search. For example, searching on the fields ti,ab,kf works when doing a multifile search in MEDLINE, Embase, and PsycINFO, but it will not work properly when searching PsycINFO alone. The kf field is not in PsycINFO so any search line that includes that field will retrieve zero results. If the kf field is removed, the search lines will run correctly. Minor modifications such as this may be required when using multifile filters in a single database.