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Find Evidence

The databases below will help you find evidence to answer your research question.

Key Databases:

Additional Resources:

Types of Evidence

A pyramid showing the increasing methodological rigor of studies, the highest rigor at the top. Top level: Systematic Reviews and Meta-analysis, refered to as secondary research. Then in decending order, randomized controlled trials, cohort studies, case-controlled studies, case series and case reports, and finally, editorials and expert opinion.

Your goal is to find the highest level and most appropriate type of evidence for your clinical question.

Systematic reviews and meta-analyses are the highest level of evidence and should always be sought after when researching patient care. See the Types of Evidence tab for more detailed descriptions of each type of study.

"Most appropriate" means the most rigorous type of research methodology which is best suited to answer a particular type of question. 

See the Types of Questions tab for more details about which types of evidence are most appropriate for different clinical questions.



Content in this box adapted from New Literacies Alliance Evidence Based Practice module, used under CC-BY-NC-SA.

Systematic Reviews and Meta-Analyses

Secondary research collects and analyzes primary research results. Systematic reviews and meta-analyses of randomized controlled trials are better at assessing strength of evidence than single studies and should be used if available. The databases below will help you find this type of research.

Case Controlled Studies

Case-Controlled Studies identify patients who have the  outcome of interest (cases) and patients without the  same outcome (controls), and look back to see if  they had the exposure of interest.

Randomized Controlled Trials

Randomized Controlled Trial (RCT) participants are randomly allocated into an experimental group or a control group and  followed over time for the variables/outcomes of interest.

Cohort Studies

A Cohort Study identifies two groups (cohorts) of patients, one that received the exposure of interest, and one that did not, and follows these cohorts forward for the outcome of interest.

Case Series and Case Reports

Case Series report on multiple patients with an  outcome of interest. No control group is  involved. A Case Report covers an  individual patient.

Editorials, Expert Opinion

Editorials offer the judgment of respected  authorities or expert committees. They are  not a research methodology.

The type of question determines the type of research studies that could legitimately offer evidence enabling you to determine an answer. Meta-analyses and systematic reviews, when available, often provide the best answers to clinical questions. However, these are not available for every question you might encounter. Below you can read about several types of clinical questions and see the types of studies that are appropriate for answering each question. When selecting studies, give priority to the studies highest on the evidence pyramid.

What disease or condition could result from exposure to this potentially harmful thing?
​Seek evidence from Randomized Controlled Trials (RCT), then Cohort Studies, then Case-Controlled Studies, and finally Case Series.

What is the patient's likely clinical course over time and what are likely complications of a particular disease or condition?
Seek evidence from Cohort Studies, then Case Control, then Case Series or Case Reports.

For a disease or condition will this treatment do more good than harm?

How does it compare to other treatment(s)?

Seek evidence from RCT.

How good is this diagnostic test at confirming or excluding a particular diagnosis?

Seek evidence from a special kind of controlled trial called a prospective, blind controlled trial in comparison to a gold standard.

Is this a risk factor for developing a particular disease or condition?

Seek evidence from RCT, then Cohort Studies, then Case Series.

Database Help

Video Length: 1:28

Used with permission from the Ronald Williams Library at Northeastern Illinois University.

Additional helpful resources

Can't access an article?

Did you find a reference to an article that looks perfect for your research, only to run into a paywall? Don't fret! The Doane Library can still get access for you. Simply fill out the InterLibrary Loan request form (link opens in new tab), and we will find another library willing to share. After 1-3 business days, a PDF copy of the article will be emailed to you!