2. What sources of evidence are there?

2.1. Secondary sources

3.1 Secondary sources

How can secondary sources help vets to be evidence-based?

A vet in practice may not have the time to do a detailed search of the primary research literature, but EBVM can help by providing secondary sources that synthesise the best available evidence to give practitioners quick answers to clinical questions.

For those with more time, EBVM provides standard methodologies to systematically search for and analyse scientific studies to answer a clinical question and create outputs that can benefit the professional community.

The main outputs of EBVM are evidence syntheses:

Systematic reviews

Systematic reviews of the scientific literature aim to find every single scientific study relating to the PICO question, allowing you to draw recommendations from the widest body of evidence.

A systematic review is performed in a highly structured way, with the question and methods clearly defined in advance to try to minimise any bias that the reviewer may have in selecting and interpreting the research.


Sometimes the systematic review is extended to include an analysis of the quantitative data sets from the research studies found (where they are sufficiently homogeneous) to provide a single estimate at the end with an indication of the confidence limits that can be applied to the combined data.

Evidence summaries

A full systematic review is a major undertaking and typically involves a team of people, taking many months to complete, and so simpler methodologies have emerged to create quick and achievable summaries of the current best evidence for a clinical question. These can have different names, such as:

  • Knowledge Summaries
  • Critically Appraised Topics (CATs)
  • BestBETs.

Clinical practice guidelines

Clinical practice guidelines are concise recommendations for healthcare professionals on how to care for patients with specific conditions, which are often based on systematic reviews or evidence syntheses.

Clinical guidelines provide a quick and easy way for busy practitioners to ensure their clinical decisions are based on the best available evidence without having to do the legwork of EBVM themselves.

Read more about how to produce these for your practice in Apply.

Manuals, textbooks and other publications

Systematic reviews and evidence summaries are still relatively uncommon in veterinary medicine, and so you will often need to search other sources, such as textbooks or the primary literature. Although textbooks and manuals use less formal methods and may not contain the most up-to-date evidence, they can still contain valuable information, and may be the best source of evidence available to answer some questions.

Read more about the Levels of Evidence in the Appraise section .

Evidence-based medicine: formal methodologies

For those wishing to create systematic reviews or evidence summaries, formal methodologies have been developed to provide standards to minimise bias.

Two key sources to be aware of:

A special issue of the journal Zoonoses and Public Health focuses on the methodology and is freely available online: Systematic Reviews and Meta-Analysis in Animal Agriculture and Veterinary Medicine .

Where you decide to search for EBVM will depend on what you are looking for:

If you are a busy practitioner, you may just want to do a quick search for evidence that others have written to see if there is a quick answer to your question. Ideally you are looking for an evidence synthesis, but in the absence of this, then you may turn to primary sources.

If you are a student or researcher, or a practitioner with more time, you might want to learn the formal methodologies of EBVM and do a comprehensive search to create a new systematic review or evidence summary.