Causality: how to prove it, and why is it important?

You wake up with a headache on a rainy day.

Did the rain cause your headache?

Or was it perhaps the late-night coffee?

You then take a homeopathic remedy, and an hour later the pain is gone.

Did the remedy cause this?

Or was it the shower you took, the placebo effect, or something else entirely?

Perhaps you don’t care? But, if we want to make progress, we ought to care and find the answers. Sorting out coincidence from actual cause is crucial for making progress. Causality is one of the most important concepts in research, because humans are naturally prone to seeing patterns where none exist. We are all easily fooled, and regularly even by ourselves. Mistaking a correlation (two things coicidentally happening in sequence) for a cause (one thing creating the other) can lead to wrong decisions, useless treatments, wasted resources, and often to significant harm. To prevent this, scientists have long relied on structured frameworks to prove when one event truly triggers another.

In the late 19th century, the German physician Robert Koch wanted a foolproof way to prove that a specific microbe caused a specific disease. He developed the “Koch’s Postulates”, a four-step checklist that transformed medicine:

1. The microbe must be present in every case of the disease.
2. The microbe must be isolated from the sick host and grown in a lab.
3. The lab-grown microbe must cause the same disease when introduced to a healthy host.
4. The microbe must be isolated again from the newly infected host.

While these rules worked beautifully for many infectious diseases, they have limits. Some viruses cannot be grown easily in a lab, and some people carry bacteria without ever getting sick. And, of course, there are many diseases that are not due to microbes.

As medicine evolved to tackle chronic, non-infectious conditions like heart disease or cancer, Koch’s checklist thus fell short. For instance, smoking causes lung cancer, but you cannot easily “isolate” smoking in a lab, nor does every smoker get cancer. To solve this riddle, the UK epidemiologist Austin Bradford Hill introduced a broader toolkit in 1965, today known as the “Bradford Hill Criteria”. Instead of a strict pass or fail test, it uses several simple viewpoints to weigh the evidence:

• Strength: Is the connection large or powerful?
• Consistency: Do different studies produce the same result?
• Temporality: Did the cause occur before the effect?
• Biological Gradient: Does more exposure lead to more severe outcomes?
• Biological plausibility: Does the connection make sense with what we already know?

Without the guardrails of causality, medicine would still be based mostly on guesswork. Koch’s postulates gave us the clarity to cure deadly infections, and the Bradford Hill criteria allowed us to take on different public health threats like tobacco. By forcing us to ask how and why things happen, these criteria allow us to ensure that medical science is built on truth rather than mere coincidence.

In the realm of so-called alternative medicine (SCAM), causality has a particularly improtant role. This is because proponents often claim causality, while science rejects it:

Homeopathy:

Proponent claim: The fact that many patients get better after taking a homeopathic remedy proves that homeopathy works.

Reality: There are many other, more convincing explanations for this outcome.

 Applied Kinesiology

Proponent claim: Muscle response strength proves nutrient deficiencies, toxin exposure, or food allergies.

Reality: No consistent relationship between muscle testing results and actual health status. The practice fails basic reliability tests; different practitioners get different results from the same patient.

Reiki

Proponent claim: Practitioners channel “healing energy” from assumed sources that improves health and prompts recovery.

Reality: No such energy exists. Well-controlled studies show Reiki performs no better than placebo. The claimed energy has no basis in physics or biology.

Acupuncture

Proponent claim: Inserting needles at specific points along “meridians” releases blocked qi and cures various conditions.

Reality: Most ot the patient-blind acupuncture trials show no difference from placebo acupuncture (needles placed randomly or not penetrating skin). Cochrane Reviews find acupuncture does no better than placebo. The meridian system has no anatomical basis.

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These 4 examples illustrate the fundamental problem: SCAM proponents routinely mistake correlation for causation, or propose causal mechanisms that have no basis in established physics, chemistry, or biology. Without satisfying the above-mentioned criteria, these claims remain unproven speculation rather than scientific fact.

To put it bluntly:

CAUSALITY MATTERS!