University Library DePaul Library

Evidence Pyramid

Depending on their purpose, design, and mode of reporting or dissemination, nursing and 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:

Strengths & Levels of Evidence

Strengths or ‘levels’ of evidence provided by different types of studies are often depicted graphically in the form of a pyramid (this example is only intended as a general representation; many variations in detail have been published in the evidence-based practice literature).

  • Lower levels of evidence include qualitative and non-experimental studies, and those that are subject to a lower level of critical appraisal.
  • Higher levels correspond to studies involving an increased degree of critical appraisal, quantitative analysis, review, assessment, and more stringent scientific methodologies.
  • The top of the pyramid represents studies subject to the highest level of critical appraisal and analysis, and corresponds to the very small proportion of all the nursing and medicine literature that lends itself to answering specific clinical questions, whether in the form of systematic reviews, meta-analyses or an evidence-based guideline resulting from combined analysis and appraisal of available evidence from all eligible sources.

It's worth noting that the 'best available' evidence for answering a particular clinical question may not be at the highest level (for example, it may not be possible to conduct controlled experiments for a particular type of problem or intervention).