What is evidence in evidence based medicine

Hint: Not Claims, Experiences, or Authority

In the world of healthcare, few phrases carry as much weight—or as much confusion—as evidence-based medicine (EBM). We hear it everywhere: in guidelines, clinical trials, hospital policies, even political debates. But beneath the surface of that familiar term lies a more complicated question: what exactly counts as evidence?

Is it a randomized controlled trial? A patient’s experience? A mechanistic explanation of how a drug works?

The need for clarity here isn’t just academic — it’s essential. That’s because the word evidence lives a double life. In everyday conversation, we use it loosely to refer to anything that supports our point of view. A personal anecdote. A strong opinion. A story we heard once that “proves” a claim. But in science and medicine, evidence implies something far more specific: information gathered through systematic observation, critical appraisal, and structured reasoning.

This tension — between rhetorical evidence (or evidence in daily conversation) and scientific evidence — lies at the core of why EBM is so often misunderstood, misapplied, or even mistrusted. And if we want to make EBM meaningful and trustworthy, we have to start by untangling what evidence really means.

Scientific Evidence: the Totality of Evidence

According to the philosophical view of evidentialism, what is reasonable to believe depends on the trustworthiness of one’s evidence, making the concept of evidence inseparable from the concept of justification.

EBM calls for careful evaluation of the totality of evidence, or body of evidence, that is, full picture of evidence — not just the pieces that are convenient or agreeable. It demands a systematic review of the best available data, taking into account the strengths and limitations of studies, the consistency of findings, and the clinical context.

So it means, unlike in casual conversation, where evidence is often loosely defined — a story, an opinion, a screenshot, a gut feeling, in EBM, evidence must be something more disciplined. It must be defined, structured, and subject to scrutiny.

“The pursuit of truth is best accomplished by examining the totality of evidence, rather than by selecting a limited sample of evidence, which is at risk of being unrepresentative and will certainly be less precise than the totality.“

Djulbegovic B, & Guyatt G (2015). Evidence-based medicine and the theory of knowledge. Guyatt G, & Rennie D, & Meade M.O., & Cook D.J.(Eds.), Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice, 3rd ed. McGraw-Hill Education. https://jamaevidence.mhmedical.com/content.aspx?bookid=847&sectionid=69031459

When we say that EBM relies on the totality of evidence, or body of evidence, we’re describing a formal process — one that requires us to comprehensively gather, critically appraise, and thoughtfully synthesize all the relevant clinical information available — This is the foundation of what we call a systematic review.

Rather than picking out a single compelling study or a convenient statistic, evidence-based medicine demands that we:

1. Define a clear clinical question – usually using a framework like PICO (Population, Intervention, Comparison, Outcome).

2. Search comprehensively for all relevant studies — across multiple databases and sources, without cherry-picking.

3. Assess the eligibility of studies – filtering the full set of results to include only those that are directly relevant to the clinical question, based on predefined inclusion and exclusion criteria.

4. Critically appraise each included study for its methodological quality, risk of bias, and applicability.

5. Synthesize the evidence across studies — narratively or statistically (via meta-analysis), depending on the nature of the data.

6. Assess the certainty or confidence in the evidence, using frameworks like GRADE, to determine how much weight the findings should carry in clinical decision-making.

This entire process reflects the process of asking question, acquiring and appraising evidence at the heart of EBM. It is not enough that a study or some studies exist. We ask in the sense of the whole picture of evidence: are they rigorous? Are they relevant? Or: How confident are we in what it tells us?`

Just as a legal case builds a judgment from a body of admissible evidence, so too does EBM seek to reach clinical judgments based on a coherent, critically evaluated body of evidence. In EBM, evidence is not just a fact or a study that appears to support a position. It refers to a systematic summary of all relevant research — with transparent methods for identifying studies, critical appraisal of their strengths and limitations, and a reasoned synthesis that considers consistency across findings and their applicability to the question at hand.

Rhetorical Evidence: The Epistemic Illiteracy

Here are some examples of misuse of evidence.

Ironically, some of the most problematic uses of the term evidence come from people who claim to be advancing “evidence-based” positions. A powerful example of this can be seen in the INTEGRITY Project, a response to Cass Review (an independent review of “gender-affirming care” in the UK). The authors of INTEGRITY Project repeatedly invoke the authority of evidence without adhering to its proper meaning within the framework of EBM. The authors of the INTEGRITY Project often appeal to evidence in a looser, more rhetorical sense — using it to refer to selective pieces of information that support their views, without acknowledging the broader or contradictory research base.

For example, they write:

“We can also speak to how the evidence informs the positive clinical outcomes that our patients experience” (p.3)

“In youth gender care, we have evidence that these medications effectively treat gender dysphoria, that young people continue these medications into adulthood” (p.15)

“Does not consider evidence that has followed patients for over a decade” (p.16)

“Sound evidence” (p.19)

McNamara, M., Baker, K., Connelly, K., Janssen, A., Olson-Kennedy, J., Pang, K. C., Scheim, A., Turban, J., & Alstott, A. (2024). An Evidence-Based Critique of “The Cass Review” on Gender-affirming Care for Adolescent Gender Dysphoria. https://web.archive.org/web/20250501184400/https://law.yale.edu/sites/default/files/documents/integrity-project_cass-response.pdf

Yet nowhere in these references is evidence presented in the form EBM requires — as a systematic review, a transparent synthesis of all relevant studies, or even a structured assessment of the quality and applicability of the data. These appeals to evidence function more like assertions of authority than products of a critical, methodologically sound process.

The American Academy of Pediatrics (AAP) recently responded to the HHS report on pediatric gender dysphoria with strong language about “evidence” backing gender-affirming care when the report was first out in May 2025. But once again, the term is invoked in a colloquial, persuasive—not systematic—sense.

In their statement, the AAP criticizes the HHS review for relying on a “narrow set of data” and for “Prioritiz[ing] opinions over dispassionate reviews of evidence” while their own message do not present a systematic appraisal of all relevant evidence, nor reference comprehensive reviews or certainty assessments — in contrast, HHS report does include a comprehensive review of available evidence. AAP also claimed “Patients, their families, and their physicians—not politicians or government officials —should be the ones to make decisions together about what care is best for them based on evidence-based, age-appropriate care. “ Again, the claim functions rhetorically, affirming credibility—without detailing the body of evidence.

When the HHS finalized their report on pediatric gender dysphoria, AMA (American Medical Association) and AAP released a joint statement on evidence-based health care in a rather rhetorical manner (of course without citing any evidence):

The American Medical Association (AMA) and the American Academy of Pediatrics (AAP) represent hundreds of thousands of physicians nationwide. Our members provide evidence-based care with a clear, singular goal of prioritizing patient health above all else.

American Academy of Pediatrics. (2025, November 19). AMA and AAP joint statement on evidence-based health care. https://www.aap.org/en/news-room/news-releases/aap/2025/ama-and-aap-joint-statement-on-evidence-based-health-care/

Even prominent public health leaders can fall into the trap of using evidence rhetorically rather than rigorously. In a recent interview, Dr. Rachel Levine, former Assistant Secretary for Health, stated:

“…emphasizing that ‘the evidence base is strong for the safety and efficacy of these treatments.’”

While this sounds authoritative, no specific studies, systematic reviews, or critical appraisals are cited in support of that claim. Once again, the phrase evidence base is used as a symbol of credibility, rather than a reference to a defined body of evidence subjected to formal evaluation.

Another illustration comes from Casey Pick, director of law and policy at the Trevor Project, in response to the HHS report on gender-affirming care. Pick stated:

“The HHS report is a rejection of decades of science, evidence, and direct experiences by young people, their doctors, and their families.”

Here again, the term evidence is used broadly, emotionally, and rhetorically. It is bundled with “science” and “direct experiences” — a grouping that may resonate politically but lacks methodological precision.

These examples reflect a broader pattern: the concept of evidence is being misused—often by those who claim to champion it. In these cases, evidence is invoked not as the product of a systematic, critical process, but as a vague assertion of credibility. It becomes a badge of authority, not a structured justification.

Too often, even reporters covering medicine for ostensibly scientific news outlets collapse the distinction between rigorously evaluated scientific evidence and rhetorically persuasive claims that only appear evidence-based. As a result, news coverage increasingly fails to fact-check rhetorical “evidence” that rests on empty assertions, appeals to authority, or unexamined experience rather than systematic evaluation. There is no better illustration of this failure than reporting in Science on reactions to the HHS report, where rhetorical appeals to “decades of science” and “strong evidence” are repeated without scrutiny of the actual evidentiary standards that evidence-based medicine demands.

This kind of misuse isn’t just careless—it’s a form of epistemic illiteracy: a failure to understand or respect what evidence actually means within the framework of EBM. In these settings, when people talk about evidence, they meant “scientific evidence”, but their evidence basis failed to meet the definition of scientific evidence, they were using “rhetorical evidence” or “evidence in daily conversation” to support their argument in the settings where scientific evidence is needed. When individuals, institutions, or even national organizations invoke evidence without engaging in systematic review, critical appraisal, or transparent synthesis, they are not practicing EBM. They are using the language of science without its method.

This matters profoundly. If evidence is allowed to mean whatever someone believes strongly or finds politically convenient, the term “evidence-based” becomes meaningless—emptied of the rigor and discipline that give it power and purpose.

To protect both the credibility of science and the quality of care, we must not only demand evidence—but demand that it be used with epistemic responsibility, not epistemic pretense.

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PS: this post does not speak to “best available evidence.“

Another side note: At times, I find myself wishing the pioneers of evidence-based medicine had chosen a Latin term to describe evidence as it is understood within EBM—one that would clearly distinguish it from the loose, rhetorical sense of “evidence” used in everyday conversation. Of course, had EBM adopted a Latin expression, it might have seemed inaccessible or unfriendly. We want people to use the concept, to talk about it, to integrate it into clinical language. The problem is not that evidence is widely discussed; it is that the term is so often misused.

Out of curiosity, I asked ChatGPT how the EBM concept of evidence—understood as the systematic evaluation of the totality of relevant data—might be expressed in Latin. Possible Latin expressions for “the totality of evidence” include:

1. Corpus evidentiae, which literally means “body of evidence”

2. Universitas argumentorum – “the totality of arguments” (more rhetorical/logical)

3. Collectio testimoniorum – “Collection of testimonies” (if the evidence is testimonial)

I further interrogated ChatGPT about the use of corpur evidentiae, it answered:

While “corpus evidentiae” is a well-formed Latin phrase meaning “body of evidence,” it’s important to note that it is a modern Latin construction. Classical Latin writers (like Cicero or Seneca) wouldn’t have used this exact phrase, but it fits modern academic, legal, or philosophical Latin very naturally.

Here are a few example sentences using corpus evidentiae in a scholarly or legal context:

🔹 Example 1: Legal context

Latin: Iudex sententiam tulit secundum corpus evidentiae.

Translation: “The judge gave his ruling according to the body of evidence.”

🔹 Example 2: Scientific or historical context

Latin: Corpus evidentiae indicat hanc theoriam esse probabilem.

Translation: “The body of evidence indicates that this theory is probable.”

🔹 Example 3: Philosophical argument

Latin: Rationabiliter loquendo, corpus evidentiae sufficit ad conclusionem firmandam.

Translation: “Reasonably speaking, the body of evidence is sufficient to support the conclusion.”