Class or level of evidence: epidemiologic basis

Introduction

Class of evidence (CoE) is a hierarchical rating system used by EBSJ and most major scientific publications for classifying the overall quality of an individual study. It is a shortcut to identifying what is likely the best (or worst) evidence on a given topic. The “classes” range from I to IV with “CoE I” representing the highest level of evidence, and “CoE IV” representing the lowest level. Assigning a CoE to an individual article is an attempt to provide the reader with a relative assessment of the research study’s risk of bias; that is, the likelihood that the results of the study are influenced by various biases rather than the intervention. This article intends to open the eyes of its readership to the many potential confounders and to look behind the claims of CoE 1.

Common sources of bias EBSJ considers when critically appraising a study include:

• Patient selection and allocation of treatment

• Intention-to-treat analysis

• Blind or independent assessment for important outcomes

• Co-interventions applied equally to study groups

• Patient follow-up rate of less than 85%

• Adequate sample size

• Controlling for possible confounding

• References

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