How to critically appraise a paper

Introduction

The Royal College of Veterinary Surgeons recognise ‘How to evaluate evidence’ as an essential day one competence required of all veterinary surgeons and critical appraisal of available evidence is a key principle of evidence-based medicine.
A vast number of veterinary papers are published every year in a variety of journals. Although many of these are in reputable journals and have been through a process of peer-review by experts, the quality is still variable. In addition, there are many sources of nonpeer-reviewed literature, including textbooks and the internet. Although formal systematic reviews are beginning to appear, it is usually up to the individual to determine the extent to which the results presented in a paper can be applied to the particular question they are interested in, and the strength of evidence of the work presented. In some instances the reader may be presented with insufficient information to appraise the reliability and these should be interpreted with caution.
Understanding the type of study that has been performed is a prerequisite to evaluation of the strength of evidence provided by the study. In addition, knowledge of the design will enable the reader critically appraising the paper to determine if the study in question has been appropriately designed and conducted, and, if not, whether this should decrease the strength of belief in the results. Clinical research studies can be divided into observational or experimental. Observational studies can be further divided into descriptive and analytical. Figure 1 shows a schematic representation of study types and the putative strength of evidence they provide. […]