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Evidence-Based Practice (EBP)

In addition to the basics of EBP and PICO, this guide answers questions about primary vs. secondary sources, where to look for evidence, and how to search to get the best results.

Types of Evidence

Hierarchy of Evidence pyramid showing primary and secondary sources

The type of question you need to answer can help you determine what type of study to look for (presented in order of preference):

 ALL CLINICAL QUESTIONS 
  • Systematic review
  • Meta-analysis
  • Clinical practice guideline

THERAPY
  • Randomized controlled trial
  • Cohort study
  • Case-control study
  • Case series

ETIOLOGY / HARM
  • Randomized controlled trial
  • Cohort study
  • Case-control study
  • Case series
DIAGNOSIS
  • Prospective, blind comparison to a gold standard
    (a type of controlled trial)
  • Cohort study
  • Cross-sectional study

PROGNOSIS
  • Cohort study
  • Case-control study
  • Case series

PREVENTION
  • Randomized controlled trial
  • Cohort study
  • Case-control study
  • Case series

See the Study Definitions tab for more about each study type. See the box below for search techniques to find different types of evidence.

Secondary sources (studies of studies; titles may contain the word summary, synopsis, or synthesis):
  • Practice Guideline (also known as Clinical Practice Guideline or Evidence-Based Guideline): A statements that includes recommendations intended to optimize patient care. Guidelines are informed by a systematic review of evidence and an assessment of the benefits and harms of alternative care options.
    • Search in: ECRI Guidelines Trust logo (create free account) • CINAHL logo • PubMed @ UMSL logo • Medline logo
  • Systematic Review: A comprehensive summary of high-quality studies examining a given topic.
    • Search in: Cochrane Library logo • CINAHL logo • PubMed @ UMSL logo • Medline logo
  • Meta-analysis: A type of systematic review in which results from available high-quality studies are statistically combined to compute a net overall effect
    • Search in: Cochrane Library logo • CINAHL logo • PubMed @ UMSL logo • Medline logo
Primary sources (original studies):
  • Randomized Controlled Trial: A carefully planned type of epidemiologic study in which participants are randomly assigned to receive a given exposure (such as a new drug or therapy) and then followed to examine the effects of the exposure on outcomes
  • Cohort Study: A type of epidemiologic study design where one or more population groups (called cohorts) are classified according to their level of exposure to a given agent/risk factor and followed over time to determine if this exposure is related to the occurrence of a disease or outcome of interest
  • Case–Control Study: A type of epidemiologic study that compares individuals who have a disease or outcome of interest (cases) with those who do not (controls). Researchers look retrospectively to evaluate how frequently exposure to a risk factor/agent is present in each group to identify the relationship between the risk factor and the disease or outcome of interest.
  • Cross-Sectional Study: A type of epidemiologic study that observes the relationship between a characteristic/risk factor (the exposure) and the prevalence of the disease or outcome of interest in a specific population at a single point in time
  • Case Series: A summary of a small group of individuals’ experience with a similar disease or outcome of interest
  • Case Reports: A summary of one individual’s experience with the disease or outcome of interest
    • Search for any of these primary sources in: Cochrane Library logo • CINAHL logo • PubMed @ UMSL logo • Medline logo

Where and How to Search

  • Multiple Types of Studies in One Search
    • Check the “Evidence-Based Practice” filter to limit your results to:
      • EBP articles, including clinical trials, meta-analyses, and systematic reviews
      • Articles from EBP journals
      • Articles about EBP

CINAHL's Evidence-Based Practice filter

  • Practice Guidelines
    • Use the “Practice Guidelines” filter under Publication Type.

CINAHL's Practice Guidelines filter under Publication Type

  • Meta-analyses
    • Use the “Meta Analysis” filter under Publication Type.
  • Systematic Reviews
    • Use the “Systematic Review” filter under Publication Type.
  • Randomized Controlled Trials
    • Use the “Randomized Controlled Trial” filter under Publication Type OR Use one of the “Therapy” filters under Clinical Queries.

CINAHL's Therapy Best Balance filter under Clinical Queries

  • Cohort Studies
    • “AND” cohort study into your search.

CINAHL search for postpartum depression and cohort study

  • Case–Control Studies
    • “AND” case control study into your search.
  • Cross-Sectional Studies
    • ​“AND” cross sectional study into your search.
  • Case Series or Case Reports
    • Use the "Case Study" filter under Publication Type OR “AND” case series or case report into your search.

NOTE: PubMed is currently updating the appearance of its website, so some of the screenshots below may look different than what you see.

  • Practice Guidelines
    • Use the "Guideline" or "Practice Guideline" filter under Article Types. (First, customize the list of article types shown, then select the desired article type to activate the filter.)

How to customize Article Types   Practice Guideline filter under Article Types

  • Meta-analyses
    • “AND” meta-analysis into your search. (This will pick up Meta-Analysis as a MeSH term and as a publication type.)

PubMed search for postpartum depression and meta-analysis

  • Systematic Reviews
    • “AND” systematic[sb] into your search. (Note: the systematic reviews subset [sb] includes meta-analyses.) OR follow the Clinical Queries link at the bottom of the homepage, search for your topic, and see the “Systematic Reviews” column.

PubMed search for hypoxia and systematic[sb]

PubMed Clinical Queries search for hypoxia

  • Randomized Controlled Trials
    • “AND” randomized controlled trial into your search. (This will pick up Randomized Controlled Trials as a MeSH term and Randomized Controlled Trial as a publication type.) OR Follow the Clinical Queries link in the center of the homepage, search for your topic, and in the “Clinical Study Categories” column choose Therapy as the Category. (Broad Scope will find a greater number of results that are less focused, whereas Narrow Scope will find fewer results that are highly focused.)
  • Cohort Studies
    • “AND” cohort study into your search. (This will pick up the MeSH term Cohort Studies and the more specific MeSH terms Follow-Up Studies, Longitudinal Studies, Prospective Studies, and Retrospective Studies under it.)
  • Case–Control Studies
    • “AND” case control study into your search. (This will pick up the MeSH term Case-Control Studies and the more specific MeSH term Retrospective Studies under it.)
  • Cross-Sectional Studies
    • ​“AND” cross sectional study into your search. (This will pick up the MeSH term Cross-Sectional Studies.)
  • Case Series or Case Reports
    • “AND” case report into your search. (This will pick up Case Reports as a publication type.)
  • Focus on Evidence-Based Medicine Titles
    • Check the “EBM Reviews” filter to limit your search to a small set of titles that apply very strict criteria and thus include high-quality evidence-based content, including systematic reviews. The titles are:
      • The Cochrane Database of Systematic Reviews
      • ACP Journal Club
      • Clinical Evidence
      • Evidence-based Mental Health
      • Evidence-based Nursing
      • Evidence report/Technology assessment

Medline (EBSCO)'s EBM Reviews filter

  • Practice Guidelines
    • Use the “Guideline” or “Practice Guideline” filter under Publication Type.

Medline (EBSCO)'s Guideline filter under Publication Type

  • Meta-analyses
    • Use the “Meta-Analysis” filter under Publication Type.
  • Systematic Reviews
    • Use the “Systematic Review” filter under Publication Type.
  • Randomized Controlled Trials
    • Use the “Randomized Controlled Trial” filter under Publication Type OR Use one of the “Therapy” filters under Clinical Queries.

Medline (EBSCO)'s Therapy Best Balance filter under Clinical Queries

  • Cohort Studies
    • “AND” cohort study into your search.
  • Case–Control Studies
    • “AND” case control study into your search.
  • Cross-Sectional Studies
    • ​“AND” cross sectional study into your search.
  • Case Series or Case Reports
    • Use the “Case Reports” or “Case Study” filter under Publication Type OR “AND” case series or case report into your search.

Medline (EBSCO) search for hypoxia and case series or case report

  • Practice Guidelines
    • Use the “Guideline” or “Practice Guideline” filter under Publication Types. (To see the filter and its choices, you will first have to click the Edit Limits button and put a checkmark next to the filter module you wish to use.)

Medline (Ovid)'s Guideline filter under Publication Types

  • Meta-analyses
    • Use the “Meta Analysis” filter under Publication Types.
  • Systematic Reviews
    • Use the “Systematic Review” filter under Publication Types.
  • Randomized Controlled Trials
    • Use the “Randomized Controlled Trial” filter under Publication Types OR Use one of the “Therapy” filters under Clinical Queries.

Medline (Ovid)'s Therapy (best balance of sensitivity and specificity) filter under Clinical Queries

  • Cohort Studies
    • “AND” cohort study into your search. To add a line to your search, you will need to use the Multi-Field Search option.
  • Case–Control Studies
    • “AND” case control study into your search. To add a line to your search, you will need to use the Multi-Field Search option.
  • Cross-Sectional Studies
    • ​“AND” cross sectional study into your search. To add a line to your search, you will need to use the Multi-Field Search option.
  • Case Series or Case Reports
    • Use the “Case Reports” filter under Publication Type OR “AND” case series into your search. To add a line to your search, you will need to use the Multi-Field Search option.

Medline (Ovid) search for hypoxia AND case series

Note: In the Cochrane Library database, selecting a suggested term from the drop-down menu puts the term inside double quotation marks, which means variations of the term will not be searched. To catch alternate spellings, plurals, etc., remove the quotation marks before running your search.

  • Meta-analyses
    • “AND” meta analysis into your search.
    • Choose the Cochrane Reviews tab in the results section.

Cochrane search for depression AND meta analysis

  • Systematic Reviews
    • Choose the Cochrane Reviews tab in the results section.
  • Randomized Controlled Trials
    • “AND” randomized controlled trial into your search.
    • Choose the Trials tab in the results section. (Note: The Trials tab normally includes both randomized and quasi-randomized controlled trials.)
  • Cohort Studies
    • “AND” cohort study into your search and change the Title Abstract Keyword field to Record Title (to eliminate trials that only reference cohort studies).
    • Choose the Trials tab in the results section.

Cochrane search for depression AND cohort study

  • Case–Control Studies
    • “AND” case-control study into your search.
    • Choose the Trials tab in the results section.
  • Cross-Sectional Studies
    • ​“AND” cross sectional study into your search.
    • Choose the Trials tab in the results section.
  • Case Series or Case Reports
    • “AND” “case study” OR “case series” into your search. Note the use of double quotation marks in the added line.
    • Choose the Trials tab in the results section.

Cochrane search for depression AND "case study" OR "case series"

  • PICO Search (BETA version)
  • Begin typing in the search bar and then select a suggested term from the drop-down menu.

Cochrane's PICO search showing menu of suggested terms

  • To the right of the search bar, you can select one of the radio buttons, which show the PICO context for reviews described with your term. For example, Diabetes Mellitus is described as both a population and an outcome, and you can focus your search on either context.

Cochrane's PICO search of Diabetes Mellitus showing population and outcome radio buttons

  • Add additional search terms by clicking the + sign. Note that the term shown below has different contexts than the first term.

Cochrane's PICO search with a second term added

  • Once you’ve run the search, you can filter your results by clicking any term from the PICO categories on the left. (Be sure to click the Show All link to see the full list.) You can also toggle open the PICO for any result, as shown below. This is a very useful tool for showing PICO in action!

Cochrane's PICO search results with filters on the left and PICOs displayed for the first result

Not Finding Enough Evidence?

What should you do if you are unable to find evidence?

Sometimes, despite your best efforts, you find few or no articles related to your clinical question. Not every PICO(T) has a perfect article, so you may need to make a decision as to what matters most to your research. If you are unable to find evidence, here are some strategies:

  • If you have flexibility in choosing a topic for your paper, do some preliminary research to see what you can find, and design your PICO(T) around the available evidence. In other words, find an alternative assessment, treatment, or service delivery option that is evidence-based.
  • Reconsider your search terms. Try making your search broader by adding more synonyms or common acronyms to your search terms.
  • Consider research from similar or related populations, interventions, or outcomes. Use your clinical judgment to decide if such information could be helpful for your paper.