A Critical Appraisal of Standard Guidelines for Grading Levels of Evidence

Abstract

Over the past 30 years, a general consensus has emerged within the medical community regarding the essential role served by grading guidelines in evaluating the quality of evidence produced by a medical research study. Specifically, consensus exists regarding the hierarchy of evidence, where randomized controlled trials (RCTs) are considered the ''gold standard'' followed by nonrandomized controlled trials (non-RCTs) and uncontrolled trials. As guidelines have become more sophisticated, processes have been developed for downgrading poorly conducted studies and upgrading strong studies. Lists of threats to internal validity have been disseminated, thereby assisting reviewers in grading studies. However, despite these many accomplishments, considerable issues remain unresolved with respect to how to evaluate the strength of evidence produced by flawed RCTs versus well-conducted non-RCTs. The purpose of this article is to evaluate existing evidence-based grading guidelines and to offer suggestions for how such guidelines may be improved.

The staircase of evidence – a new metaphor displaying the core principles of Evidence-based Veterinary Medicine

“…These methods vary in regard of the certainty that the information is free from bias (Gugiu et al, 2010). Scientific evidence is the product of appropriately designed and carefully controlled research studies (Sargeant et al, 2014a).…”

“…The hierarchy of evidence is a categorisation of sources with the aim to highlight those that are most likely to avoid a biased outcomes (Cockcroft et al, 2003). Level 1 evidence is obtained from systematic reviews and metaanalyses of randomized controlled clinical trials (RCT) or single RCT with narrow confidence intervals (Gugiu et al, 2010;Holmes et al, 2007). Ideally, evidence should be derived from multiple studies investigating the same research question (Sargeant et al, 2014a).…”

“…Metaanalyses summarize and combine information, weight and analyse the results of independent studies relating to a specific topic. Hence by increasing the sample size and statistical power the precision of an estimated outcome can be increased (Lean et al, 2009 (Gugiu et al, 2010). This appraisal should address aspects like enrolment criteria, the allocation in experimental designs, blinding, the sample size, statistical methodologies and the objectiveness in the discussion of the results.…”

Choosing the Best Evidence to Guide Clinical Practice: Application of AACN Levels of Evidence

“…10,11 The rigor of a study refers to the strict precision or exactness of the design. In general, findings from experimental research are considered stronger than findings from nonexperimental studies, and similar findings from more than 1 study are considered stronger than results of single studies.…”

“…Systematic reviews of randomized controlled trials are considered the highest level of evidence, despite the inability to provide answers to all questions in clinical practice. 11,12 For example, AACN and other organizations have done extensive research on healthy work environments. This topic would not be examined in a randomized controlled trial because of ethical and practical considerations.…”