Module 4 · Thinking skills · Strong evidence

Thinking critically about health claims

How to judge a headline, a post or a product that promises to change your health.

8 min read · Level: Intermediate · Free — no account needed to read

The idea

Health is full of confident claims: a food that burns fat, a supplement that boosts focus, a morning routine that changes everything, a headline saying coffee is good — or bad — for you. Thinking critically about them protects your time, money and sometimes your health.

A few questions go a long way. Is this one study or many? Was it an experiment, or did researchers only observe a link? (People who do X may also differ in many other ways.) How big was the effect, and who was studied? Who is making the claim, and do they profit from it? Does it promise a lot, fast, for everyone?

Strong evidence usually comes from many studies pointing the same way, including randomised trials and reviews that combine them. Big organisations like WHO and national health bodies summarise that evidence. That is why every lesson here shows an evidence label and its sources — so you can judge for yourself.

Why it works

Without these questions, you are at the mercy of whoever is most confident or most marketed. With them, you can tell a promising idea from a proven one.

A real example

The situation

Tariq sees a video claiming a new supplement “doubles focus” and is about to buy three months’ supply.

What happened

He asks the questions: the “study” is a single small trial funded by the company, the effect was modest, and the seller profits. He decides to spend the money on better sleep — earplugs and blackout curtains — which has much stronger evidence behind it.

The takeaway

Six questions saved his money and pointed him to something more likely to help.

Use this when you are…

• you see a health headline or post that sounds exciting
• someone is selling a health product
• two sources contradict each other

Common mistakes

• Treating one study as settled truth.
• Confusing “linked with” and “causes”.
• Trusting a claim because the person is confident, famous or has a title.

What the evidence says

Strong evidence: Many good-quality studies, usually including randomised trials and reviews that pool them, point the same way. Guidelines tend to recommend it.

The principles of evidence-based medicine — randomised trials, reviews that pool studies, and attention to bias and effect size — are well established. Applying them to everyday claims takes practice, and even good evidence can change over time.

Where this comes from: Evidence-based medicine and critical appraisal; World Health Organization (WHO).

Fields that study this: Public health.

Try it now: Check one claim

1. Find a health claim you have seen recently.
2. Ask: one study or many? Experiment or observation? How big an effect?
3. Ask: who is saying it, and do they profit from it?

Questions to think about

• Which health claim have you believed without checking?
• Where do you usually get your health information, and how reliable is it?

Try this today

The next health headline you see today, ask whether it is one study or many.

Afterwards, ask yourself

What did checking a claim reveal about it?

Words in this lesson

• Correlation vs causation — Two things happening together (correlation) doesn’t prove one causes the other (causation). A third factor, or reverse direction, may explain the link.
• Randomised controlled trial — A study where people are randomly assigned to receive a treatment or a comparison, so differences in results can be credited to the treatment.
• Meta-analysis — A study that combines the results of many studies on the same question to get a more reliable overall answer.
• Placebo — A treatment with no active ingredient. Comparing a real treatment with a placebo shows how much of an effect comes from the treatment itself.