Day in and day out, we all take steps to reduce the risks in our lives. We wear our seatbelts to avoid getting hurt in a car crash. We brush our teeth to protect them from cavities and we carry umbrellas to cut down on the risk of getting soaked in a storm. Even though we take these steps every day, most of us don't spend much time thinking about risk. It's actually an important concept that's worth exploring, especially when it comes to matters of health and science. "Risk" in these fields can have different meanings. Knowing some of the basic types of risk can help you understand your chances of developing breast cancer and the steps you can take to lower your chances of getting it.

Absolute Risk
The most basic type of risk is absolute risk, which is a person's chance of developing a specific disease over a certain period of time. Absolute risk is estimated by looking at a large group of people who are similar in some respect (in terms of age, for example) and counting the number of people in the group who develop the disease in question over a specified time period.

For example, if we followed 100,000 women between the ages of 20 and 29 for one year, about 4 would develop breast cancer during this period. This means that the one-year absolute risk of breast cancer for a 20- to 29-year-old woman is 4 per 100,000 women, or 1 per 25,000 women. Another way to say this is that the chances of developing breast cancer in the next year are 4 in 100,000 (or 1 in 25,000) for the average 20- to 29-year-old woman.

In another example, if we followed 100,000 women aged 70 to 74 for a one-year period, about 400 of them would develop breast cancer. This means the one-year absolute risk of breast cancer for a 70- to 74-year-old woman is 400 per 100,000 women, or 1 per 250 women.

Knowing the absolute risk of a disease can help you prioritize the health risks in your life. In the examples above, for instance, we see that the absolute risk of breast cancer is low in young women and much higher in older women.

Lifetime Risk
One absolute risk that many people are familiar with is the lifetime risk of breast cancer. Currently, women in the U.S. have a "1 in 8," or about 12 percent, lifetime risk of breast cancer [5]. This statistic means that for every 8 American women who live to be age 85, one of them will be diagnosed with breast cancer during her lifetime. The lifetime risk of breast cancer is much higher than the one-year risk of breast cancer. This is because the lifetime risk is a type of summing, or adding up, of all the one-year absolute risks over a woman's life span, up to age 85.

Risk Factors
Anything that affects a person's absolute risk of developing a disease is called a risk factor. A risk factor can be anything from a lifestyle choice (such as diet) to a genetic component (such as family history) to an environmental exposure (such as radiation). For instance, lack of exercise is a risk factor for breast cancer. Women who are not regularly active have a higher risk of breast cancer than women who are regularly active.

Relative Risk
Though the term "relative risk" may not sound familiar, you usually see or hear about relative risks all the time in news stories about health. A relative risk is a generalized way to present the increase or decrease in risk that's due to a certain risk factor.

A relative risk is calculated by taking the ratio of two absolute risks. The numerator (the top number in the ratio) is the absolute risk among those with the risk factor. The denominator (the bottom number) is the absolute risk among those without the risk factor. When the absolute risk of those with the factor is divided by the absolute risk of those without the factor, the number you get is the relative risk.

Courtesy: Susan G Komen Race for the Cure
www.komen.org