Which is an example of level IV evidence

Rating System for the Hierarchy of Evidence to Guide Clinical Interventions

Level I - Evidence from a systematic review or meta-analysis of all relevant randomized controlled trials (RCTs)

Level II - Evidence obtained from well-designed RCTs

Level III - Evidence obtained from well-designed controlled trials without randomization

Level IV - Evidence from well-designed case-control and cohort studies

Level V - Evidence from systematic reviews of descriptive and qualitative studies

Level VI - Evidence from single descriptive or qualitative studies

Level VII - Evidence from the opinion of authorities and/or reports of expert committees

Source: Melnyk BM. Implementing the Evidence-Based Practice (EBP) Competencies in Healthcare : A Practical Guide to Improving Quality, Safety, and Outcomes. ; 2016. (Table 1.1, p. 11)

Study Design Tree

Q1. What was the aim of the study?

To simply describe a population (PO questions) 

• Descriptive

To quantify the relationship between factors (PICO questions) 

• Analytic

Q2. If analytic, was the intervention randomly allocated?

Yes? 

• RCT

No?

• Observational study

For observational study the main types will then depend on the timing of the measurement of outcome, so our third question is:

Q3. When were the outcomes determined?

Some time after the exposure or intervention?

• Cohort study (‘prospective study’)

At the same time as the exposure or intervention?

• Cross sectional study or survey

Before the exposure was determined?

• Case-control study (‘retrospective study’ based on recall of the exposure)

Source: Centre for Evidence Based Medicine: Study Designs.https://www.cebm.ox.ac.uk/resources/ebm-tools/study-designs

Rating System for the Hierarchy of Evidence: Quantitative Questions

Level I: Evidence from a systematic review of all relevant randomized controlled trials (RCT's), or evidence-based clinical practice guidelines based on systematic reviews of RCT's

Level II: Evidence obtained from at least one well-designed Randomized Controlled Trial (RCT)

Level III: Evidence obtained from well-designed controlled trials without randomization, quasi-experimental

Level IV: Evidence from well-designed case-control and cohort studies

Level V: Evidence from systematic reviews of descriptive and qualitative studies

Level VI: Evidence from a single descriptive or qualitative study

Level VII: Evidence from the opinion of authorities and/or reports of expert committees

Melnyk, B., & Fineout-Overholt, E. (2011). Evidence-based practice in nursing & healthcare: A guide to best practice (2nd ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins, p. 10.

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:

CINAHL (EBSCO)

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.

MEDLINE (OVID)

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.

PsycINFO (EBSCO)

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.

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