Levels of Evidence in Research Articles

While doing a project, you may find different levels of credibility to report scientific results. For example, using a systematic review or expert opinion to cite an argument is not the same. It is almost logical that the former shows more accurate results than the latter, that the information ultimately comes from the individual.

For example, in the field of medicine and health care, it is important that professionals not only have access to information, but also have the tools to determine which evidence is stronger and more reliable, and have the confidence to diagnose and treat patients.

Five levels of evidence

As physicians and other scientists in various fields of study increased their need to know what kind of research could expect the best clinical evidence, experts ranked this evidence to help them identify the best sources of information to answer their questions.

Evidence ranking criteria are based on the design, methodology, validity, and application of different types of studies and is called “levels of evidence” or “levels of the hierarchy of evidence.” By organizing a well-defined hierarchy of evidence, academics sought to help scientists ensure that they used the findings of high-quality evidence in their work or practice. For Physicians, whose daily activity depends on available clinical evidence to support decision-making, this helps them to know which evidence to trust the most.

Level 1 (higher quality of evidence)

This category includes High quality randomized trial or prospective study; testing of previously developed diagnostic criteria on consecutive patients; sensible costs and alternatives; values obtained from many studies with multiway sensitivity analyses; systematic review of Level I (randomized controlled trial) RCTs and Level I studies.

Level 2

Level 2 entails Prospective comparative study; Retrospective study; Untreated controls from RCT. A lower quality prospective study; Development of diagnostic criteria in consecutive patients; Reasonable costs and alternatives; Values obtained from limited studies; Multivariate sensitivity analysis; Systematic review of second or first level studies with conflicting results.

Level 3

Case study (therapeutic and prognostic studies); Retrospective comparative study; Study of non-consecutive patients without reference are in level 3. Moreover, analysis based on alternatives and limited costs, poor estimates as well as any systematic review of Level 3 can be in this level.

Level 4

This level includes series of cases, such as Case study (diagnostic studies), Poor reference standard, Analysis without sensitivity to analysis.

Level 5 (lower quality of evidence, Expert opinion)

Level 1 and Level 2 include filtered information, meaning that an author has gathered evidence from well-designed studies with valid results and presented findings and conclusions evaluated by renowned experts. So, they are credible and strong enough to serve researchers and scientists. On the other hand, Levels 3, 4, and 5 contain evidence from unfiltered information. Since this evidence has not been evaluated by experts, it may be suspicious, but it is not necessarily false or inaccurate.

Examples of levels of evidence:

Systematic reviews: A comprehensive summary of all available literature on a particular topic. So, authors should provide critical reviews of all of this literature when drafting a systematic review rather than providing a simple list. Researchers who produce systematic reviews have their own criteria for locating a collection of the evaluation literature.

Meta-analysis: uses quantitative methods to synthesize a combination of the results of independent studies. Typically, they act as an overview of clinical trials.

Randomized and controlled trial (RCT): A clinical trial in which participants or individuals (those who agree to participate in a trial) are randomly divided into groups. So, the control group receive a placebo while the other group takes the medication. As a result, this type of research is the key to learning about the effectiveness of a drug.

Cohort studies: A longitudinal study plan in which one or more specimens called cohorts (individuals with a defining characteristic, such as a disease) are exposed to an event, monitored prospectively, and evaluated at predefined intervals. These studies are good for linking diseases to risk factors and health consequences.