Imagine reading a health headline that says:
“New treatment cuts your risk of a heart attack by 50%!”
That sounds impressive. But before deciding how much the treatment might help you, there’s one important question to ask:
50% of what?
The answer depends on two things: your risk before treatment and your risk afterward. Understanding the difference between relative benefit and absolute benefit can help you see what a health claim really means.
The Same Result, Two Different Ways to Tell the Story
Imagine a study following 1,000 people for five years.
Without treatment, 20 people have a heart attack. With treatment, only 10 do.
The results can be described in two ways:
- Relative benefit: 50%. The treatment cuts the risk of a heart attack in half.
- Absolute benefit: 1 percentage point. The risk falls from 2% to 1%—10 fewer heart attacks per 1,000 people over five years.
Both statements are correct. But they tell different parts of the story.
The relative figure describes the reduction compared with the original risk. The absolute figure shows the actual change in risk.
A headline emphasizing a 50% reduction sounds dramatic. The absolute numbers give you a clearer picture of how much difference the treatment made in this group.
Neither figure is wrong. The problem is hearing only the impressive percentage without seeing the actual numbers.
The Starting Risk Changes Everything
Now imagine another group of 1,000 people whose starting risk is much higher.
Without treatment, 200 people have a heart attack. With treatment, 100 do.
Once again, the treatment cuts the risk by 50%. But this time, it prevents 100 heart attacks per 1,000 people rather than 10.
Compare the results:
| Measure | Lower starting risk | Higher starting risk |
|---|---|---|
| Risk without treatment | 2% | 20% |
| Risk with treatment | 1% | 10% |
| Relative risk reduction | 50% | 50% |
| Absolute risk reduction | 1 percentage point | 10 percentage points |
| Fewer cases per 1,000 | 10 | 100 |
The relative benefit is identical, but the absolute benefit is ten times greater in the higher-risk group.
That’s the key point: the same relative reduction can make a much bigger practical difference when the starting risk is higher.
What Does This Mean for You?
Your personal risk may be different from the risk of the people in a study.
Age, family history, existing health conditions, and other factors can all affect your starting risk. And the people in a study might not closely resemble you.
That’s why a treatment that offers a substantial benefit to someone at high risk might offer a much smaller absolute benefit to someone at low risk—even if the relative reduction is similar.
Of course, the benefit is only one part of the decision. Possible side effects, cost, inconvenience, and the seriousness of the condition also matter.
The point isn’t to dismiss a treatment because its absolute benefit is small. A small reduction can still be worthwhile, particularly when the potential outcome is serious and the treatment has few downsides.
The point is to understand what you’re gaining so you can weigh the benefits against the risks.
How to Read the Next Health Headline
Whenever you see a claim such as “reduces risk by 30%,” “cuts the chance of disease in half,” or “reduces your risk by 80%,” ask three questions:
- What was the risk before treatment?
- What was the risk after treatment?
- Over what period were those results measured?
Look for the actual numbers, not just the relative percentage. If the headline doesn’t provide them, look for the original study or a reliable explanation of its findings.
And remember: a result measured over one year is not the same as a result measured over ten years.
The Watchdog Takeaway
Relative benefit tells you how much a risk falls in percentage terms. Absolute benefit tells you how much the risk actually falls.
Both are important, but the relative percentage alone can make a modest benefit sound enormous. To understand what a treatment might mean for you, you need to know the starting risk, the risk after treatment, and the period involved.
The next time you hear “cuts your risk by 50%,” ask: “What was my risk to begin with, and what would it be after treatment?”
That’s how you get past the headline and closer to the truth.
Sources
Evidence: Strong. This article is general information, not personal medical advice.