RATING SYSTEM FOR THE HIERARCHY OF EVIDENCE TO GUIDE CLINICAL INTERVENTIONS
The quality or certainty of evidence is an important factor in making decisions about clinical interventions. Different types of evidence have different strengths and weaknesses, and some are more reliable than others. To help clinicians and researchers evaluate and compare the evidence, various rating systems have been developed. One of the most widely used and accepted systems is the GRADE approach, which stands for Grading of Recommendations Assessment, Development and Evaluation (GRADE Working Group, 2004).
The GRADE approach rates the quality of evidence for each outcome across studies, based on four criteria: risk of bias, inconsistency, indirectness, and imprecision. The quality of evidence can be rated as high, moderate, low, or very low. High quality evidence means that we are very confident that the true effect lies close to that of the estimate of the effect. Very low quality evidence means that we are very uncertain about the estimate of the effect (Guyatt et al., 2008).
The GRADE approach also provides a system for grading the strength of recommendations, based on the balance between benefits and harms, values and preferences, resource use, and quality of evidence. The strength of recommendations can be either strong or weak (conditional). Strong recommendations mean that most informed patients would choose the recommended course of action, and that clinicians can structure their interactions with patients accordingly. Weak recommendations mean that different choices will be appropriate for different patients, and that clinicians must help each patient arrive at a management decision consistent with their values and preferences (Guyatt et al., 2008).
The following table summarizes the rating system for the hierarchy of evidence to guide clinical interventions, based on the GRADE approach:
| Level | Explanation |
| — | — |
| I | Evidence from a systematic review or meta-analysis of all relevant randomized controlled trials (RCTs) |
| II | Evidence obtained from well-designed RCTs |
| III | Evidence obtained from well-designed controlled trials without randomization |
| IV | Evidence from well-designed case-control and cohort studies |
| V | Evidence from systematic reviews of descriptive and qualitative studies |
| VI | Evidence from single descriptive or qualitative studies |
| VII | Evidence from the opinion of authorities and/or reports of expert committees |
A systematic review is a study that summarizes the results of multiple primary studies on a specific question or topic, using explicit methods to identify, select, appraise, and synthesize the evidence. A meta-analysis is a statistical technique that combines the results of multiple primary studies to produce a pooled estimate of the effect (Higgins & Green, 2011).
A randomized controlled trial is a study that randomly assigns participants to an intervention group or a control group, and compares the outcomes between the groups. Randomization reduces the risk of confounding factors that may affect the results. A well-designed RCT has adequate sample size, allocation concealment, blinding, and follow-up (Higgins & Green, 2011).
A controlled trial without randomization is a study that assigns participants to an intervention group or a control group based on some criteria other than randomization, such as convenience, availability, or preference. This type of study has a higher risk of bias than an RCT, because the groups may not be comparable at baseline or may be influenced by other factors during the study (Higgins & Green, 2011).
A case-control study is a study that compares participants who have a specific outcome (cases) with participants who do not have that outcome (controls), and looks back in time to identify possible exposures or risk factors that may be associated with the outcome. A cohort study is a study that follows a group of participants who share a common exposure or characteristic (cohort) over time, and compares their outcomes with another group of participants who do not have that exposure or characteristic (comparison group). Both case-control and cohort studies are observational studies, which means that they do not intervene or manipulate the exposure or outcome variables. They can provide evidence about associations, but not causation (Higgins & Green, 2011).
A systematic review of descriptive and qualitative studies is a study that summarizes the results of multiple primary studies that describe or explore a phenomenon or experience, using explicit methods to identify, select, appraise, and synthesize the evidence. A descriptive study is a study that provides information about the characteristics or distribution of a population or phenomenon without testing a hypothesis. A qualitative study is a study that uses methods such as interviews, focus groups, observations, or document analysis to collect and analyze data in words rather than numbers (Higgins & Green, 2011).
A single descriptive or qualitative study is a primary study that describes or explores a phenomenon or experience, using methods such as interviews, focus groups, observations, or document analysis to collect and analyze data in words rather than numbers (Higgins & Green, 2011).
The opinion of authorities and/or reports of expert committees is a source of evidence that is based on the judgment or experience of experts in the field, rather than on empirical data. This type of evidence may be useful when there is no or limited research evidence available, but it is subject to bias and variability (Higgins & Green, 2011).
The rating system for the hierarchy of evidence to guide clinical interventions can help clinicians and researchers to appraise and synthesize the available evidence, and to make informed and evidence-based decisions. However, it is important to note that the quality of evidence is not the only factor that influences the strength of recommendations. Other factors, such as the balance between benefits and harms, values and preferences, resource use, and feasibility, also need to be considered in the context of each specific question and setting (Guyatt et al., 2008).
GRADE Working Group. (2004). Grading quality of evidence and strength of recommendations. BMJ, 328(7454), 1490. https://doi.org/10.1136/bmj.328.7454.1490
Guyatt, G. H., Oxman, A. D., Vist, G. E., Kunz, R., Falck-Ytter, Y., Alonso-Coello, P., & Schünemann, H. J. (2008). GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. BMJ, 336(7650), 924–926. https://doi.org/10.1136/bmj.39489.470347.AD
Higgins, J. P., & Green, S. (Eds.). (2011). Cochrane handbook for systematic reviews of interventions (Version 5.1.0). The Cochrane Collaboration. https://training.cochrane.org/handbook