Understanding Risk:

What Do Those Headlines Really Mean?

Tips from the National Institute on Aging

What does risk mean when it’s part of 

health news? Every day, news stories 

report medical findings. How risk is 

described can change how you handle 

your health. Perhaps a certain medicine 

carries a 50% increased risk of stroke. That 

sounds scary. Does it mean that 50%—or 

half—of everyone taking the drug will 

have a stroke? No, it doesn’t. Let’s start by 

assuming that in every 1,000 people who 

are not taking the medicine, two people 

will have a stroke. A 50% increase means 

1 more person, or 3 total out of 1,000, will 

have a stroke while on this drug. Stroke 

can be a devastating illness, but maybe 3 

out of 1,000 doesn’t seem as big a risk as 

50% sounds. And that risk might be an 

acceptable one if the medicine could help 

your health problem. 

But how can you know if that increased risk 

even applies to you? This fact sheet provides 

background you can use to make sense of 

research results. Better understanding of risk 

could help you sort out the news that 

might be important to you from other 

reports that might be of interest, but would 

not be a reason to change how you take 

care of your health.

Are All Research Studies the 

Same?

No, there are different types of studies. 

Some take place in a laboratory, others 

involve animals, and some look at people. 

A scientist might start with a question—

maybe whether a new drug cures a bacterial 

infection—and set up an experiment to 

answer it. In this experiment, the scientist 

grows the bacteria in the laboratory and 

then adds the new drug. Usually, there is 

also a control—that is, the same bacteria 

are grown in the same way but not exposed 

to the new drug. The scientist then watches 

the treated bacteria and the untreated bacteria. If the treated bacteria are dying while 

the untreated ones are still growing, that 

“Risk” is the chance that something bad will happen—like catching the flu 

or being hit by a car when crossing the street. Risk does not mean 

that something bad will definitely happen. 

National Institute on Aging 

National Institutes of health

U.S. Department of Health and Human Services
could mean the drug is working. Scientists 

might next test the drug in laboratory 

animals and later in people.

Which Studies Involve People?

When studying people, scientists often use 

observational studies. In these, scientists 

keep track of a group of people for several 

years. It’s useful to be able to observe 

the same people over a long time period. 

By looking at what those people have 

in common, as well as how they differ, 

scientists can discover clues as to who 

develops a disease and who does not. What 

they learn can suggest the path for more 

research.

However, observational studies are limited 

since they may not be able to prove a cause 

and effect. Many things can affect an 

outcome. For example, if an observational 

study finds that a group of people who 

chose to eat carrots every day had less 

heart disease than a group who ate no 

carrots, that does not mean that eating 

carrots definitely prevents heart disease. 

Perhaps the group who ate carrots already 

had a heart-healthy diet or maybe they 

exercised regularly. Because the scientists 

were only observing the carrot-eating 

behavior, they did not see other factors 

(both obvious and subtle) that might affect 

the results.

On the other hand, it is also possible that 

since the scientists didn’t ask about family 

history, they didn’t know that the group 

who didn’t eat carrots had many more 

cases of heart disease in their family tree 

than the carrot-eating group—a factor that 

could have a big influence on the development of heart disease. Further research is 

often needed to help prove what directly 

affected health. 

What Comes Next?

The results of laboratory experiments 

and observational studies, when looked at 

together, might point to the next research 

step. For example, perhaps a new cholesterol-lowering drug has been tested in the 

laboratory. And, studies using the drug in 

animals suggest that it lowers cholesterol 

levels. Because observational studies have 

shown that people with high cholesterol 

levels are more likely to have heart attacks, 

scientists want to know if heart attacks 

could be prevented by using the new drug 

to lower cholesterol levels.

To prove whether or not an intervention, 

such as this drug, might work in people, 

scientists use another kind of research 

study, the randomized controlled clinical 

trial. A clinical trial often involves thousands 

of people. 

First, the research team looks for volunteers, who are assigned to study groups 

by chance (randomized). For each group 

that receives a treatment, there is a control 

group that gets a placebo. A placebo looks 

just like the treatment or drug being 

tested but contains no active medicine. 

Sometimes people call a placebo a “sugar 

pill.” In addition, the study is masked.

This means that neither the doctors nor 

the volunteers know who is getting the 

test treatment or the placebo. In the case 

of the cholesterol-lowering drug, for 

example, study investigators keep track 

of cholesterol levels and heart attacks in 

each group over a predetermined period 

of time. They also watch for side effects 

of the drug. At the end of the study, the 

results are analyzed, and everyone learns 

who was getting the treatment and who the 

placebo. If there were fewer heart attacks 

in the group receiving the test drug, it 

Understanding Risk: What do those headlines really mean?

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Tips from the National Institute on AginG

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might mean lowering cholesterol levels 

with this new drug prevents heart attacks.

How Are the Results Explained?

To describe how well this fictional drug 

prevented heart attacks, scientists might 

talk about how it affects someone’s risk

of heart attack. Were people receiving the 

drug more or less likely to have a heart 

attack than people who got the placebo? 

To explain the findings, scientists report 

risk, either increased risk or reduced risk, 

which is sometimes referred to as the 

“benefit” of the intervention. Risk can be 

explained in several ways. These include 

relative risk and absolute risk. 

When the difference in risk between two 

groups is described as “relative,” it is 

usually shown as a percent—like the 50% 

increased risk of stroke described at the 

start of this tip sheet.

When that difference is described as 

“absolute,” it is nothing more than a 

number found by subtraction—again at the 

start of this tip sheet, an absolute risk of 1 in 

1,000 people. It is important to understand 

what these numbers mean because how they 

are presented to you can affect how you “feel” 

about the finding and whether you decide to 

change your health-related behavior.

Let’s first look at relative and absolute 

differences without thinking about health 

risk. For example, a soccer team is selling 

boxes of cookies to raise money for new 

uniforms. Emily sold 66 boxes, and Sara 

sold 60 boxes. Emily sold 10% more than 

Sara—that’s the relative difference. Stated 

another way, Emily sold six more boxes 

than Sara, the absolute difference. When 

you hear that Emily sold 10% more than 

Sara, that might sound like a good margin. 

But if you understand that meant only six 

boxes, you might also think that, really, it 

may not be that much—with just a little 

more effort, Sara might have tied or beat 

Emily!

Relative Risk and Your Health

The results of the cholesterol drug trial 

might be described in terms of relative risk. 

This compares the chance that a person 

who takes the new medicine will have a 

heart attack to the chance that someone 

not taking the medicine will have one. It 

tells us how much larger or smaller the 

risk of heart attack is while using the test 

drug. Maybe the study showed the chance

of heart attacks in the group receiving the 

placebo is 50% greater than the chance

of heart attacks in people taking the test 

medicine. That does not mean half of all 

those not taking the test drug had heart 

attacks. Instead, this is what it means: Let’s 

say the group receiving the test medicine 

had a 2% risk of heart attack. Then the 

untreated group would have a 3% risk of 

heart attack—50% larger than the 2% risk 

in the treated group. 

Emily Sara

Number of 

boxes sold 66 60

Relative 

difference 10% more than Sara

Absolute 

difference 6 boxes more than Sara
Understanding Risk: What do those headlines really mean?

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Absolute Risk and Your Health

Absolute risk tells you the number of health 

problems that happened or might have 

been prevented because of a treatment. In 

our imaginary study of a new cholesterol 

drug, maybe there were 2 heart attacks in 

100 people taking the drug and 3 heart 

attacks in a similar group taking the placebo. 

That is, for every 100 people not using it, 

there would probably be 1 more heart 

attack (3 minus 2). That’s the absolute 

risk. Some people find absolute risk easier 

to use for their own healthcare decisions 

than a relative risk percentage.

Putting Risk to Work

How can you use risk information when 

making healthcare decisions? To illustrate, 

let’s look at Julia, who recently learned 

that she has lost bone mass and might 

develop osteoporosis. Exercising and 

getting more calcium and vitamin D are 

slowing her bone loss. But her doctor also 

suggested she use a drug to help prevent 

osteoporosis. Several drugs are available. 

Julia asked her doctor how well each one 

would protect her from breaking a bone. 

For each medicine, the doctor gave her a 

risk percentage (relative risk) and also told 

her how many more people who don’t take 

each drug break a bone than those who 

do take the drug (absolute risk). They also 

talked about the possible side effects of 

each drug. 

Julia found it helpful to think about risk 

in a slightly different way—looking not 

only at the risk of breaking a bone, but also 

the chances of not breaking a bone. For 

example, if people who take osteoporosis 

drug A have a 30% risk of breaking a bone, 

that also means they have a 70% risk of not

breaking a bone. People taking osteoporosis drug B have a 60% risk of breaking 

a bone or a 40% chance of not breaking a 

bone. Both prevent fractures, but drug A 

appears to be more effective. 

Another approach to making a difficult 

decision about treatment or lifestyle 

changes is to try stepping back a little. 

It can be useful to look at the risks and 

benefits, and think about how you would 

decide for someone else. Perhaps you can 

more objectively weigh benefits versus 

risks when you are not thinking about 

yourself.

Ask Yourself

The next time you learn about a new medical finding, here are some questions to ask:

1. Was this a study in the laboratory, 

in animals, or in people? Results of 

research in people are more likely to 

apply to you.

2. Does the study include enough 

people like you? Were the people 

in the study a similar age, sex, 

education level, income group, and 

ethnic background as you? Did they 

have the same health concerns and 

lifestyle?

3. Was it a randomized controlled 

clinical trial involving thousands 

of people? These trials give scientists 

the most useful information about 

whether a treatment or a lifestyle 

change is effective. But they are the 

most costly to do, and scientists hope 

to find more efficient, less expensive 

ways to study this in the future.
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Tips from the National Institute on Aging

4. Where was the research done? 

Scientists at a medical school or large 

hospital, for example, often lead 

complex experiments or have more 

experience with the topic. Many 

large clinical trials involve several 

institutions or clinics, but the results 

may be reported by one coordinating 

group.

5. Are the reported results in line with 

previous studies? Sometimes a study 

will report something very different 

from what scientists expected to 

find. In medical research, the road 

to understanding is never straight. 

Research findings may differ, but the 

trend of research should be in the 

same direction. Any result needs to 

be repeated elsewhere several times 

before it might be considered truly 

valid.

6. What does it mean when the results 

of a study are described as 

statistically significant? Statistically 

significant means the finding is not 

likely to be due to chance. It does 

not always mean, however, that the 

finding is important for your health 

decisions. 

7. Are the results presented in an easyto-understand way? Absolute risk, 

relative risk, or some other easy-tounderstand number should be used.

8. If a new treatment was tested, were 

there side effects? Sometimes the side 

effects are almost as serious as the 

disease. Or, the drug might worsen a 

different health problem.

9. Who paid for the research? Do they

stand to gain financially from 

positive or negative results?

Sometimes the Federal government 

or a nonprofit foundation helps fund 

research costs. They looked at the 

plans for the project and decided 

it was worthy of support, but they 

will not make money as a result. If a 

drug is being tested, the study might 

be partly or fully paid for by the 

company that is developing the drug.

10. Where did you see or hear the 

results? Is the newspaper, magazine, 

website, or radio or television 

station a reliable source of medical 

news? Some media outlets have 

special science reporters on staff. 

They are trained to interpret medical 

findings. These news reports can 

alert you about the latest research 

results, but you should talk to 

your doctor to help you judge how 

accurate the reports are.

Interested in a Clinical Trial?

To learn more about clinical trials, 

the National Institute on Aging has 

two publications—Clinical Trials and 

Older People—Tips from the National 

Institute on Aging and Participating in 

Alzheimer’s Disease Clinical Trials and 

Studies. Both are available at www.nia.

nih.gov/health, or you can get a print 

copy by calling 1-800-222-2225. 

If you would like to volunteer for 

a clinical trial, you will find many 

listed at www.clinicaltrials.gov.
Understanding Risk: What do those headlines really mean?

To order free publications (in English or Spanish) or sign up for email alerts, go to:

www.nia.nih.gov/health

Visit NIHSeniorHealth (www.nihseniorhealth.gov), a senior-friendly website from the National Institute on Aging and 

the National Library of Medicine. This website has health and wellness information for older adults. Special features make it 

simple to use. For example, you can click on a button to have the text read out loud or to make the type larger.

For more information about health and aging, contact: 

National Institute on Aging Information Center

P.O. Box 8057

Gaithersburg, MD 20898-8057

1-800-222-2225 (toll-free)

1-800-222-4225 (TTY/toll-free)

www.nia.nih.gov

www.nia.nih.gov/espanol

SEPTEMBER 2011

NIH Publication no. 11-7482

The Bottom Line

Ask your doctor to help you understand 

the results and what they could mean 

for your health. The results of one study 

need to be considered along with similar 

research by other scientists at different 

locations over a period of time before they 

are accepted as general medical practice. 

Progress in medical research takes many 

years, and understanding what new discoveries mean to you will help you improve, as 

well as protect, your health.