LibGuides: Evaluating Health Information: Understanding What Risk Percentages Mean

Making Sense of

Health Risk Numbers

Sometimes health information presents the likelihood of something happening (or not happening) as an absolute risk percentage. We've all seen these assertions ("1 out of 1000 people will..." etc.).

Medical research, however, more often talks about a percentage increase or decrease to the absolute risk. This gets confusing, especially if the information doesn't state what the absolute risk numbers are to start with. For the sake of explanation, let's say the absolute risk of stroke is 2% (2 people out of 100). A new drug lowers the risk by 50%; sounds fantastic! But that means only half of 2%, - 1%, or 1 person out of 100 - actually benefits from that drug.

Really understanding the importance of research findings might take some calculations.

Reporting the findings: Absolute vs relative risk (Health News Review)

Tip: Correlation Does Not Mean Causation

Don't make assumptions!

It is so very tempting to assume that if there seems to be a relationship between two factors, then somehow the first one is causing the second. But that's a false assumption. It takes much more focused research to actually prove cause. Clinical research often claims that there are correlations between different variables, or even that A) might predict B), but beware jumping to the conclusion that A) causes B).

If you find information that asserts A) really does cause B), does it explain the mechanism for how that happens? If not, don't TRUST that explanation without many other confirming sources. Maybe assuming that correlation = cause isn't Hallowe'en-level scary, but when it comes to health matters, it can be deadly.

The National Cancer Institute gives us this definition of the phrase "risk factor":

"Something that increases the chance of developing a disease.

Some examples of risk factors for cancer are age, a family history of certain cancers, use of tobacco products, being exposed to radiation or certain chemicals, infection with certain viruses or bacteria, and certain genetic changes."

Risk factors generally fall into one of these categories:

* Fixed risk factors, which can't be changed directly, like --

age
genetics (family history) or anatomy
medical history (injuries, surgeries, diseases that happened in the past

* Variable risk factors, which can change over time. Because it's possible to modify these risk factors, medical research focuses on them a lot. These can be further divided into --

environmental risk factors (exposure to pollution or chemicals, limited diet, unsafe drinking water, physical or emotional abuse, exposure to racism, poverty (or wealth), housing insecurity, easy access to healthcare services, etc. - even the amount of sunlight per day)
risk behaviors (doing things we know could endanger our health, like use tobacco, get drunk, drive unsafely, ride a bike without a helmet, keep a firearm in the house without locking it away, not practicing safe sex, etc.)
lifestyle risk factors (diet, sleep patterns, physical activity, occasional alcohol use, etc.)
iatrogenic risk factors (risk of a drug or medical treatment causing harm, even if it works as intended)

Some risk factors - like obesity, eating disorders, addiction, or working in dangerous occupations - are probably a combination. For example, obesity is likely to be affected by lifestyle, environment, possibly genetics or medical treatments, and perhaps even the environment of our gut microbiome.

Because it's assumed that lifestyle factors are under our control (not completely accurate), current medical practice in the U.S. directs a lot of attention to: tobacco use, alcohol consumption, physical activity, sleep, and overweight / obese body weight.