RELATIVE RISK CAN BE DECEIVING
To illustrate how much this can matter: In 1995, the UK... issued a warning that third generation oral contraceptive pills increased the risk of thrombosis by 100%.
What that meant was that the risk of getting thrombosis -- potentially life-threatening blood clots in the legs or lungs -- went from one in 7,000 for women taking second generation birth control pills to two in 7,000 for those taking the third generation variety.
Not a huge risk, then.
But a 100% risk increase sounds quite ominous.
The warning scared many women away from the pill (as psychologist Gerd Gigerenzer describes in his book Risk Savvy).
One result was an estimated 13,000 additional abortions the following year in England and Wales.
Another was, ironically, a lot of thrombosis cases -- pregnancies and abortions are much more likely to bring on the condition than does taking a third generation birth control pill.
5% CHANCE OF COLORECTAL CANCER, 2% CHANCE OF DIEING FROM IT
Information about relative risk (or percentage increase in risk, such as the 18% above) can be misleading, then, unless it's presented in the context of absolute risk.
So what's the absolute risk of getting colorectal cancer?
According to the National Cancer Institute, men 60 and younger face almost a 5% chance of getting colorectal cancer in their lifetimes, and a greater than 2% chance of dying from it. For women it's about 4.5% and 1.9%.
COLORECTAL CANCER COMMON, BUT LATE IN LIFE
Colorectal cancer, then, is a relatively common and deadly disease. It tends to hit people later in life, when they're eventually going to die of something in any case. But still, it's worth trying to avoid.
Let's say you're a man, you have about a 5% chance of eventually getting colorectal cancer, and you up your bacon consumption by two pieces a day.
That increases your cancer risk to almost 6% -- not a trivial jump.