You can limit your subject search results by study types to locate research based on level of evidence. Below are tips for utilizing limits or filters for the following databases:
To limit your subject search results by research study types, click on “Show More” to the left of your search set. Find the “Publication Type” box and select the desired type of study, such as Clinical Trial, Randomized Controlled Trial or Systematic Review. Hold down the “Ctrl” key to select more than one publication type. Click on “Save” to see your search results limited by publication type.
For study types that are not listed as a “Publication Type” search the “CINAHL Headings” for the study type. For example, search for Prospective Studies (a.k.a. Cohort Studies). Combine the search for the study type with your previous search.
To limit your search results to include specific study types, click on the “Additional Limits” button at the bottom of the blue “Limits” box. Select the search that you want to limit. Use the menu labeled “Publication Types” to select Controlled Clinical Trial, Multicenter Study, or Randomized Controlled Trial. You can select all four at once by holding the “Ctrl” key as you click on the types. Click on “Limit A Search” to see your results listed on the main search page, in the search history box. Click on “Display” to see the list of results. Search directly for study types not listed as a “Publication Type" and combine the search for the study type with your previous search.
PubMed @ UM (MEDLINE)
To limit your search results to specific study types, utilize the “Filters” available on the left of the result. Select the desired “Article Types” such as Clinical Trial, Meta Analysis, or Randomized Controlled Trial. Click on “more…” to see the full list of Article Types and have the option to check which articles types to “show” on the filter list. Once on the list, select the desired Article Types to filter the search results. Search directly for study types that are not listed as “Article Types" and combine with your previous search.
To limit your search results to specific study types or methodologies, click on the “Show More” option. Use the box labeled “Methodology” to select Empirical Study, Follow-up Study, or Quantitative Study. Hold down the “Ctrl” key to select more than one. Click on “Search” to see your search results limited by methodology. Search directly for methodologies not listed, and then combine with your previous search.
Level 1 - Systematic review & meta-analysis of randomized controlled trials; clinical guidelines based on systematic reviews or meta-analyses
Level 2 - One or more randomized controlled trials
Level 3 - Controlled trial (no randomization)
Level 4 - Case-control or cohort study
Level 5 - Systematic review of descriptive & qualitative studies
Level 6 - Single descriptive or qualitative study
Level 7 - Expert opinion
Melnyk, B.M. & Fineout-Overholt, E. (2015). "Box 1.3: Rating system for the hierarchy of evidence for intervention/treatment questions" in Evidence-based practice in nursing & healthcare: A guide to best practice (3rd ed.) (pp. 11). Philadelphia, PA: Wolters Kluwer Health.