Dulaney-Browne Library: Levels of Evidence: Levels of Evidence

Systematic Review articles present evidence gathered from the review of previously published studies. They may include only randomized controlled trials (level 1 evidence) or a wider variety of studies (level 5 evidence).

Look for key words including:

Systematic Review
Meta-Synthesis
Meta-Analysis

Also review abstracts and articles to determine if the review uses randomized controlled trials and counts as level 1 evidence or uses a wider variety of studies and counts as level 5 evidence.

Top database choices:

CINAHL Ultimate This link opens in a new window
The most important nursing and allied health journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.
Cochrane Database of Systematic Reviews This link opens in a new window
full text systematic reviews on health care research prepared by Cochrane, often including meta-analysis
Medline with Full Text This link opens in a new window
The most important medicine journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.

Controlled trial articles describe a single study of an intervention which is carried out on one group and compared to a second "control" group to draw conclusions about the effectiveness of the intervention.

Controlled trials may be randomized (level 2) or non-randomized (level 3).

Look for key words including:

Randomized Controlled Trials
Controlled Trials
Clinical Controlled Trial
Treatment Outcome/Clinical Trial

Also review abstracts and articles to determine if the trial uses randomization and counts as level 2 evidence or does not use randomization and counts as level 3 evidence.

Top database choices:

CINAHL Ultimate This link opens in a new window
The most important nursing and allied health journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.
Cochrane Central Register of Controlled Trials This link opens in a new window
descriptions of reports of controlled trials, including journal articles and reports from trial registers that include studies whose results have not yet been published
Medline with Full Text This link opens in a new window
The most important medicine journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.

Case Control Study articles present observations comparing "case" patients with a condition to "control" patients without the condition.

Cohort Study articles present observations over time of groups or "cohorts" of people to evaluate outcomes based on common experiences.

Look for key words including:

Case Control Study
Cohort Study
Retrospective Cohort Study
Prospective Cohort Study

Top database choices:

CINAHL Ultimate This link opens in a new window
The most important nursing and allied health journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.
Medline with Full Text This link opens in a new window
The most important medicine journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.

Descriptive studies do not include an experiment or intervention.

Case report articles provide a profile of a subject or group of subjects with a condition of interest.

Cross-sectional studies provide a profile of a disease or condition in a specific population.

Qualitative studies focus on experiences, stories, or perspectives of the subjects.

Look for key words including:

Descriptive
Qualitative
Experiences
Perspectives
Ethnography
Grounded Theory

Also review abstracts and articles to determine if the methods described are descriptive or qualitative.

Top database choices:

CINAHL Ultimate This link opens in a new window
The most important nursing and allied health journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.
Medline with Full Text This link opens in a new window
The most important medicine journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.

Expert opinion appears in the literature as editorials and commentaries.

Look for key words including:

Editorial
Commentary
Communication
Comment

Top database choices:

CINAHL Ultimate This link opens in a new window
The most important nursing and allied health journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.
Medline with Full Text This link opens in a new window
The most important medicine journal article database. Many articles are full-text, others may be available in the library or through Interlibrary Loan.

Definitions

Systematic review & meta-analysis of randomized controlled trials; clinical guidelines based on systematic reviews or meta-analyses
One or more randomized controlled trials
Controlled trial (no randomization)
Case-control or cohort study
Systematic review of descriptive & qualitative studies
Single descriptive or qualitative study
Expert opinion

Source: Melnyk, B.M. & Fineout-Overholt, E. (2011). Evidence-based practice in nursing and healthcare: A guide to best practice. Philadelphia: Lippincott, Williams & Wilkins.