Evidence Grading

• Systematic reviews and meta-analyses of veterinary RCTs
• Large multi-center RCTs in the target species
• ACVIM/AAHA/RECOVER consensus statements based on systematic evidence review

Level II: Strong Evidence

• Single-center RCTs in the target species
• Well-designed prospective cohort studies with adequate sample sizes
• Board-certified specialist textbooks (Ettinger's, Plumb's, Nelson & Couto, Fossum's, Tilley's)

Level III: Moderate Evidence

• Retrospective case series (n>20)
• Cross-sectional studies
• Case-control studies
• Evidence extrapolated from closely related species

Level IV: Weak Evidence

• Small case series (n<20)
• Single case reports
• Extrapolation from human medicine without species-specific validation
• Expert opinion without systematic evidence review

Level V: Lowest Evidence

• In vitro studies only
• Anecdotal reports
• Manufacturer-sponsored data without independent validation
• Social media or forum consensus

Important: Why Textbooks Rank Higher in Veterinary Medicine

In human medicine, clinical guidelines based on systematic reviews supersede textbooks. In veterinary medicine, textbooks authored by board-certified specialists remain the most comprehensive, curated synthesis of clinical knowledge for many conditions. This is because:

1. Veterinary RCTs are scarce for many conditions.
2. Textbook authors are typically the leading specialists who synthesize decades of clinical experience alongside available evidence.
3. Textbooks are updated on regular cycles and reviewed by peers.
4. For many clinical questions, a specialist textbook chapter is the best available evidence.

This does NOT mean textbooks are infallible. When high-quality RCTs or systematic reviews exist, they should take precedence.

Workflow

1. Identify the clinical claim or recommendation to be graded.
2. Determine the highest-quality evidence source supporting it.
3. Assign an evidence level (I-V).
4. Note the species-specificity of the evidence (same species, related species, or cross-species extrapolation).
5. Note recency (evidence older than 10 years may not reflect current best practice).
6. Communicate the evidence grade alongside the recommendation.

Output Format

**Recommendation:** [Clinical recommendation]
**Evidence Level:** [I-V]
**Source:** [Citation]
**Species-specific:** [Yes/No -- if No, note the source species]
**Recency:** [Publication year]
**Note:** [Any caveats about evidence quality]

Limitations

• Evidence grading is a framework for comparing relative evidence quality, not an absolute measure of truth.
• Absence of evidence is not evidence of absence. Many effective veterinary treatments lack formal RCT validation.
• Clinical experience and local practice patterns legitimately influence treatment decisions alongside formal evidence.