Do not believe all experts: hierarchy of scientific evidence

Science is the tool that has allowed human beings to understand the world around them and to be able to apply everything they have learned to benefit from it.

Advances in science are fundamental as they influence every aspect of life, from finding cures for diseases to discovering solutions to environmental challenges and enabling sustainable living.

Science is neither bad nor good in and of itself; this depends on its interpretation and the purposes for which it is used. On the other hand, it will ALWAYS be necessary for us as a society to approach science to gain the necessary knowledge and choose among all the options available to us, whether personal, political, or professional.

At Baïa, we invite you to delve into the fascinating world of research.

With so much information available today, it's dangerous to rely on opinions and erroneous data, and that's why we want to teach you how to find the best available evidence.

Scientific evidence is classified depending on the design of the studies from which it comes.

This facilitates the search for the best available evidence, as it gives it a hierarchical ranking that serves as a guide for decision-making. Based on this evidence, a recommendation should be made based on the strength of the supporting evidence.

In 1979, the Canadian Task Force on Period Health Examination created the first evidence hierarchy for the evaluation of preventive measures.

Since then, there has been a significant increase in proposals and classifications for ranking evidence and their grades of recommendation. There are 11 proposals that are currently most widely used (CTFPHC, Sackett, USPSTF, CEBM, GRADE, SIGN, NICE, NHMRC, PCCRP, ADA, and ACCF/AHA), but to avoid confusion, we'll summarize Sackett's.

This classification was proposed by epidemiologist David L. Sackett and is the one generally used. It ranks evidence from 1 to 5, with 1 being "the best" evidence and 5 being "worse or less good."

Most experts agree that the higher up the pyramid, the less likely the methodology and results are to be biased.

Meta-analyses and systematic reviews are at the top of the pyramid, while expert opinions and anecdotal experience are at the bottom.

1. Systematic reviews They are characterized by using a scientific, transparent and detailed methodology in which the studies and evidence available on a specific question are collected, reviewed and evaluated and the results are summarized. A meta-analysis It differs from a systematic review in that it uses statistical methods to combine the results of the studies.
2. Randomized controlled trials Also known as randomized clinical trials, participants are randomly assigned to separate groups to compare treatments or interventions, one of which can be a placebo, no intervention, or the standard intervention.
3. Cohort trials They are a type of observational research with the purpose of determining the association between exposure factors and development of the event of interest both prospectively and retrospectively (natural history, survival, factors and prognoses).
4. Case-control studies Two groups of people are compared: one with the disease or condition and another similar group who do not have the disease or condition, and the two are compared. This is different from a cohort study because in this case, individuals are selected based on their disease and their past is observed. In a cohort study, individuals are selected based on exposure and a wait-and-see approach is taken to see whether or not the disease or condition develops.
5. Cross-sectional studies They are observational studies where variables collected over a given period of time from a given population are analyzed.
6. Editorials and expert opinions: In medical science, the personal opinion of professionals should be of little importance, since relying on personal opinions is dangerous, especially if they claim to be "experts" without scientific studies to back them up.

You'd be lying to yourself if you thought that for every question you had, you were going to go find scientific evidence and classify it according to Sackett (although let me tell you, this would be an incredible idea).

What we want you to take away is the importance of basing our practice on data and scientific studies with the highest level of evidence. Today, there are "experts" on every corner, and we often listen to them and take their information as law when, in reality, they occupy the lowest place within Evidence-Based Medicine.

As long as we continue to base our knowledge on opinions and consensus and ignore clinical trials and meta-analyses, we will be acting in an outdated, uninformed, and sometimes even dangerous manner.

Don't just say, "I talked to a doctor about it, and he says it's dangerous for your health," or "I talked to an expert about it, and he says it's the absolute cure."

Previously, we had to rely on animal models, experiences, anecdotes, and evolutionary logic, but with all the evidence we have today and quality studies, we can no longer be satisfied with the past.

If you have any questions or want to contribute something, we look forward to hearing from you in the comments!