In 1979, the canadian task force published a document on the Periodic Health Examination. This was when the levels of evidence were initially explained. The basic purpose of the report was to come up with good enough suggestions on the periodic health exam and the foundation of those recommendations had to be evidence in the medical literature. The writers of the paper created a system that helped them rate evidence while trying to decipher the efficiency and effectiveness of a specific intervention. This hierarchical system was known as the four levels of evidence. The evidence was taken into consideration when grading recommendations (these grading recommendations are mentioned in the article).
The Four Levels Of Evidence
Systematic Reviews And Randomized Control Trials
The basic task of someone who is performing a systematic review is to ask a particular clinical question, to carry out an extensive and thorough literature review, remove any research that is not up to the mark, and try to make suggestions for practice based on the research that has been carried out exceptionally. It is only experimental or quantitative studies that fall under the umbrella of systematic reviews; most of the time, such studies involve randomized controlled trials.
A randomized controlled trial (RCT) is a potential experiment based on quantitative analysis and drawing parallels and is accomplished under a controlled environment with a random distribution of interferences to the comparison groups. Out of all research methods, a randomized controlled trial is the most accurate, potent, and yet onerous. It figures out whether or not there is a cause–effect relationship between an intervention and its result.
When gauging the validity, productivity and security of any intervention, an RCT can be used which will then in turn produce high‐quality evidence. Moreover, randomized controlled trials go pretty hand in hand with systematic review and meta‐analysis, thus contributing to a strong foundation for arranging the evidence produced by such investigations.
Cohort Studies
Cohort studies are a kind of long-term research plan that proceeds from the exposure to the outcome. There are two kings of cohort studies, prospective and retrospective.
A prospective cohort study is also known as a ‘concurrent cohort study’. It is when the subjects who are part of the experiment are tracked for some time and the eventual results that the researcher is interested in, are recorded.
On the other hand, in a retrospective cohort study, both the exposure and the results of it have already taken place at the beginning of the research. Retrospective cohort study takes less time and is less expensive as compared to a prospective cohort study, the former is still more vulnerable when it comes to the impact of bias.
Case Control Studies
Case control studies are somewhat similar to an observational study. In this level of evidence, two current groups showing contradictory results are recognized and contrasted with each other on the basis of some presumed unusual feature. Usually in case control studies, a comparison is drawn between the ‘cases’ and the ‘controls’ (the controls do not have the same conditions as the cases but are somewhat similar) which is then used to pinpoint aspects that may lead to a medical condition. As compared to a randomized controlled trial, a case control study needs lesser resources but then it also gives fewer evidence for unusual conjectures. Since it only gives an odd ratio, a case control study it is not a very reliable method of calculating strength of association in comparison to a relative risk.
Case-Based Reasoning Or Expert Opinion
The case-based reasoning (or CBR) method is built around using one’s experience in order to tackle new problems by modifying any successful tactic used to solve identical problems in the past. CBR includes problem solving, addressing memories, planning and learning. Moreover, it also creates a base for a more modern technology of intelligent computer systems (or artificial intelligence) that can evolve according to their surroundings and counter any complications. In case based reasoning, the “intelligent” usage of one’s knowledge and experiences from hurdles that have already been overcome, or cases that have already been solved, depends on the presumption that the identical any two problems are, the more identical their answers will be.
The Levels Of Evidence Pyramid
The levels of evidence pyramid supplies you with a way to picture both, the quality of evidence and how much evidence is accessible. As an example, let us take a look at systematic reviews. They are situated at the top of the pyramid, which means that along with being the highest level of evidence, systematic reviews are also the least common. If we start moving towards the base of the pyramid, the amount of evidence you will receive from that particular method will increase, but the quality of the evidence will fall.
What Is The Highest Level Of Evidence
The highest level of evidence is the Randomized Controlled Trials due to the fact that they are unbiased and have the least risks of any systemic failure. Following list shows the four levels of evidence, from the highest to the lowest:
1) Systematic Reviews And Randomized Controlled Trials
2) Cohort Studies
3) Case Control Studies
4) Case-Based Reasoning Or Expert Opinion
Grading Of Recommendation, Assessment, Development, And Evaluation (GRADE)
Codes
Grading of recommendation involves four codes:
- A
- B
- C
- D
Quality Of Evidence
Each of these four codes, represent a particular quality of the evidence that has been gathered:
- Code A signifies a high quality of evidence;
- Code B signifies a moderate quality of evidence;
- Code C signifies a low quality of evidence; and
- Code D signifies a very low quality of evidence
Definitions Of Level Of Evidence A, B, C and D
Code A
This occurs when any further research is most probably not going to affect the confidence that the researcher has in the estimate of the results. Code A usually takes place after one had conducted several high-quality experiments and produced consistent results. It involves one huge , high-quality trial.
Code B
Code B is when conducting some more research might have an important and positive impact on the confidence of the researcher when it comes to the estimate of the results. Moreover, further research might even alter the estimate. Typically, Code B involves one high-quality study along with several studies with some restrictions.
Code C
This is when there is a very huge chance of further research having an important impact on the researchers confidence in the result estimations. It plays a crucial part in an experiment and can change the estimated result. Code C research involves one or more studies with serious restrictions.
Code D
In this grade recommendation, any estimation of the results calculated is extremely unclear. It requires expert opinion as there is no direct research proof. Moreover, further research in code D involves more than one study, analysis, and multiple reviews, with extreme restrictions.
Conclusion
The four levels of evidence discussed in this article are important for everyone to learn especially for those who want to produce a critically acclaimed piece of research. This level of evidence hierarchy falls under the umbrella of evidence-based medicine (or EBM). It focuses on trying to come up with solid evidence and using that evidence to make clinical assumptions and even decisions. Usually clinical researchers are encouraged to find the highest level of evidence, which is the RCT when it comes to answering clinical questions.
