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DVM2 VOCE 2017 Library Workshop

Module 3 - Evidence-based veterinary medicine & Critical appraisal

Evidence-Based Veterinary Medicine is: "The conscientious, explicit and judicious use of the best scientific evidence to inform clinical judgements with a view to improving clinical outcome at the level of the individual case.
 From "Statistics for Veterinary and Animal Science", by Aviva Petrie & Paul Watson, Blackwell Publishing, 2006.

 In order to establish the validity of an article on  therapy, the following questions may be asked:

  • Was there a clearly defined research question?
  • Was the assignment of patients to treatments randomised and was it blinded (i.e. owners and clinicians unaware of which treatment was used)?
  • Were all the patients accounted for at the end of the study?
  • Was there adequate follow-up?
  • Were the groups for comparison treated equally throughout, and were they comparable?

From "Handbook of Evidence-Based Veterinary Medicine", by Peter Cockcroft & Mark Holmes, Blackwell Publishing,  p.86, 2003.

Hierarchy of published evidence.

The Evidence-Based Pyramid is divided into levels. Each ascending level represents a different type of study design and corresponds to increasing rigor, quality, and reliability of the evidence.  In other words, as we ascend through these different study designs, we become more confident that their results are accurate, have less chance of statistical error, and minimise bias from confounding variables that could have influenced the results. Hierarchies are guides to the power of the designs, but the quality of the individual studies needs to be critically appraised. There is overlap between the different levels in the hierarchy since a well-designed cohort study may provide better evidence than a poorly designed RCT

This pyramid of evidence has been adapted from Handbook of Evidence-Based Veterinary Medicine. [From Peter Cockcroft and Mark Holmes, Blackwell Publishing (Oxford, 2003), 68].

Studies can be divided into descriptive studies and explanatory studies.

Descriptive studies are designed to record observations. They do not compare the observations to a control group and therefore no attempt should be made to explain causation or make conclusions about treatment effects. They can be used for formulating hypotheses that can be tested by more appropriate and powerful explanatory designed studies.

Explanatory (or Analytic) studies differ from descriptive studies as they compare two groups. The comparison may be between diseased and non-diseased animals with regard to a disease risk factor or it may be an evaluation of a new treatment where one group is treated with a traditional  treatment while the other group receives the new treatment. The groups are then examined and outcomes compared. There are two main types of explanatory study: experimental and observational. In experimental studies the animals are randomly allocated to different treatment groups. In observational studies the groups are created from the treatments the animals have had or are receiving.

The Centre for Evidence Based Medicine is a not-for-profit organisation dedicated to the practice, teaching and dissemination of high quality evidence based medicine to improve healthcare in everyday clinical practice. They provide a comprehensive analysis of the advantages and disadvantages of the different kinds of trials and study designs. Go to their webpage for further detail.


The following websites will give you further information about Evidence Based Veterinary Medicine.

BestBETs for Vets - A BET is a simple review of the current best evidence available to answer very common and specific clinical questions

Centre for Evidence-based Veterinary Medicine - This  website provides information about on-going projects and useful resources for the veterinary profession to promote the use of Evidence-based Veterinary Medicine principles.

VetSRev - database of veterinary systematic reviews - The database of systematic reviews in veterinary medicine and science

Evidence based Medicine- Human

Centre for Evidence Based Medicine - The Centre for Evidence Based Medicine is a not-for-profit organisation dedicated to the practice, teaching and dissemination of high quality evidence based medicine to improve healthcare in everyday clinical practice.

Critical Appraisal Skills Programme (CASP) - CASP offers critical appraisal skills training, workshops and tools. These help you read and check health research for trustworthiness, results & relevance.

 CASP  Checklists - Scroll down for some Study Design definitions

CASP E-learning Modules - These modules guide you through the process of  learning how to find the evidence, how to assess the validity and reliability of the published research.