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Veterinary - Evidence-based Veterinary Medicine: Evidence pyramid

evidence based pyramid

Adapted from EBM Pyramid and EBM Page Generator, copyright 2006 Trustees of Dartmouth College and Yale University.


Filtered resources

  • Summarize, examine and appraise the evidence of multiple individual studies (unfiltered resources)
  • Often make recommendations for practice
  • Be aware that filtered resources are only good as the individual studies (unfiltered resources) examined and the rigor with which the review was conducted

Unfiltered resources

  • Original research studies that provide evidence related to a particular research topic
  • Generally unfiltered resources are published journal articles (peer reviewed journal articles have been vetted by experts in the field)
  • For unfiltered sources, you need to take extra care to appraise the resources to ensure they are valid and reliable

Types of study defined

Meta-analysis A statistical technique that summarises the results of several studies in a single weighted estimate, in which more weight is given to results of studies with more events and sometimes to studies of higher quality.
Meta-analysis typically refers to the quantitative methods (usually involving weighting) used to integrate data from trials. This is logically distinct from a systematic review, which is defined by an explicitly systematic search and appraisal of the literature with or without an accompanying meta-analysis of the data. Meta-analysis is also distinct from data pooling, which is based purely on the raw data.

Systematic review - A review in which specified and appropriate methods have been used to identify, appraise, and summarize studies addressing a defined question. It can, but need not, involve meta-analysis). 

Critically Appraised Topics (CAT) - provide a quick and succinct assessment of what is known (and not known) in the scientific literature about an intervention or practical issue by using a systematic methodology to search and critically appraise primary studies. However, in order to be quick, a CAT makes concessions in relation to the breadth, depth and comprehensiveness of the search. Due to these limitations, a CAT is more prone to selection bias than a systematic review or rapid evidence assessment. 

Randomized controlled trial (RCT) A trial in which participants are randomly assigned to two or more groups: at least one (the experimental group) receiving an intervention that is being tested and another (the comparison or control group) receiving an alternative treatment or placebo. This design allows an assessment of the relative effects of interventions.

Cohort study A non-experimental study design that follows a group of people (a cohort), and then looks at how events differ among people within the group. A study that examines a cohort, which differs in respect to exposure to some suspected risk factor (e.g., smoking), is useful for trying to ascertain whether exposure is likely to cause specified events (e.g., lung cancer). Prospective cohort studies (which track participants forward in time) are more reliable than retrospective cohort studies.

Case-control study A study design that examines a group of people who have experienced an event (usually an adverse event) and a group of people who have not experienced the same event, and looks at how exposure to suspect (usually noxious) agents differed between the two groups. This type of study design is most useful for trying to ascertain the cause of rare events, such as rare cancers.
Case-control studies can only generate odds ratios (OR) and not a relative risk (RR). Case-control studies provide weaker evidence than cohort studies but are more reliable than case series.

Case series Analysis of a series of people with the disease (there is no comparison group in case series). Case series provide weaker evidence than case-control studies.


Definitions from BMJ's Glossary of EBM Terms and CEBMa Guideline for Critically Appraised Topics in Management and Organizations

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