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Morris Library

Evidence-Based Practice: Evidence Levels & Types

A tutorial on evidence-based practice.

Evidence Pyramid

Depending on their purpose, design, and mode of reporting or dissemination, health-related research studies can be ranked according to the strength of evidence they provide, with the sources of strongest evidence at the top, and the weakest at the bottom. Source: Depaul University Library

 

pyramid of levels of evidence

Secondary Sources: studies of studies

Systematic Review

  • Identifies, appraises, and synthesizes all empirical evidence that meets pre-specified eligibility criteria
  • Methods section outlines a detailed search strategy used to identify and appraise articles
  • May include a meta-analysis, but not required (see Meta-Analysis below)

Meta-Analysis

  • A subset of systematic reviews: uses quantitative methods to combine the results of independent studies and synthesize the summaries and conclusions
  • Methods section outlines a detailed search strategy used to identify and appraise articles; often surveys clinical trials
  • Can be conducted independently, or as a part of a systematic review
  • All meta-analyses are systematic reviews, but not all systematic reviews are meta-analyses

Evidence-Based Guideline

  • Provides a brief summary of evidence for a general clinical question or condition
  • Produced by professional health care organizations, practices, and agencies that systematically gather, appraise, and combine the evidence
  • Click on the 'Evidence-Based Care Sheets' link located at the top of the CINAHL screen to find short overviews of evidence-based care recommendations covering 140 or more health care topics.

screenshot of CINAHL database

 

Meta-Synthesis or Qualitative Synthesis (Systematic Review of Qualitative or Descriptive Studies)

  • a systematic review of qualitative or descriptive studies, low strength level

Source: Depaul University Library

Primary Sources: original studies

Randomized Controlled Trial

  • Experiment where individuals are randomly assigned to an experimental or control group to test the value or efficiency of a treatment or intervention

Non-Randomized Controlled Clinical Trial (Quasi-Experimental)

  • Involves one or more test treatments, at least one control treatment, specified outcome measures for evaluating the studied intervention, and a bias-free method for assigning patients to the test treatment

Case-Control or Case-Comparison Study (Non-Experimental)

  • Individuals with a particular condition or disease (the cases) are selected for comparison with individuals who do not have the condition or disease (the controls)

Cohort Study (Non-Experimental)

  • Identifies subsets (cohorts) of a defined population
  • Cohorts may or may not be exposed to factors that researchers hypothesize will influence the probability that participants will have a particular disease or other outcome
  • Researchers follow cohorts in an attempt to determine distinguishing subgroup characteristics

Further Reading

Strongest Sources of Evidence

Systematic Review

A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit methods aimed at minimizing bias, in order to produce more reliable findings that can be used to inform decision making (Cochrane Library Handbook Section 1.2.2). When such studies involve specifically quantitative techniques to combine and analyze data from multiple independent studies, they'd be referred to as a 'meta analysis.'

 Meta-Analysis

Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature (PubMed Medical Subject Heading).

All meta-analyses are systematic reviews, but not all systematic reviews are meta-analyses.

 Evidence-Based Guideline

Developed by any of a large number of different professional health care organizations, practices and agencies that systematically gather, appraise and combine health care evidence and create statements designed to assist practitioner and patient decision-making.

Click on the 'Evidence-Based Care Sheets' link located at the top of the CINAHL screen to find short overviews of evidence-based care recommendations covering 140 or more health care topics.

screenshot of CINAHL database