WEDNESDAY, May 16, 2007 (HealthDay News) -- Many women will tell you their risk of developing breast cancer is higher than their risk of developing heart disease.
In fact, the opposite is true.
Also, when people are sad after hearing about a serious health problem, they tend to believe they're at higher risk for that condition. When they are in a happy mood, they perceive their risk as being lower.
These are just two examples in a new study of the errors and biases exhibited by individuals, including doctors and other health-care professionals, in the way they perceive cancer risk.
That perception, in turn, affects what they do to safeguard -- or jeopardize -- their health.
"A lot of decisions people make regarding their health are based on perceptions of risk," said atudy author William M. P. Klein, an associate professor of psychology at the University of Pittsburgh. "If a person believes he or she is at high risk, that may have implications for whether that person gets screened or engages in dietary changes, so it's important to have an accurate perception of risk."
"There are biases on both sides of the equation," Klein continued. "People overestimate and underestimate risk, and both have potentially negative health consequences."
Klein's study is published in the May/June issue of CA: A Cancer Journal for Clinicians, a publication of the American Cancer Society.
Not surprisingly, many Americans suffer greatly from innumeracy -- a difficulty with grasping numbers.
"It's very clear that people have trouble understanding percentages and proportions, and they think about numerators differently than they should," Klein said.
For example, people often don't understand that the percentage of smokers who get lung cancer is much lower than the percentage of people with lung cancer who smoke.
And when told that eight out of 100 patients may die during a particular procedure, many people focus on the eight who die as opposed to the 92 who do not. In one example, college undergraduates were shown two bowls of jelly beans: one with one red jelly bean out of 10 and the other with 7 red jelly beans out of 100. When told they would win a prize if they managed to select a red jelly bean out of the bowl, most chose the second bowl, even though it offered a lower probability of winning.
Emotions also play a major role in risk perception and consequent behavior.
Generally, people will assess their risk for a given danger to be lower than average, because they don't want to feel vulnerable, the study reported.
For most people, the pain of loss usually outweighs the pleasure of gain. This could explain why women are more likely to get a mammogram when they are given "loss-based" messages as opposed to "gain-framed" messages.
Other emotional influences also play a part.
"When people try to forecast their emotional reactions in the future, they tend to be wrong. They tend to overestimate how devastated they'll be by something," Klein said. "They don't realize they have a 'psychological immune system' that can be brought to bear."
So, a woman who has just received a positive genetic test for the breast cancer gene will be trying to decide whether to have a double mastectomy or whether to have children, and she will be trying to figure out how she will feel when it is all over.
"This has tremendous implications for decision-making," Klein said.
All people share these biases, the experts said, including health-care professionals and others with advanced degrees.
One medical expert agreed.
"We as doctors and as patients overestimate people's ability to be like Dr. Spock. We bring our emotions to the table," said Dr. Christian Cable, an assistant professor of internal medicine at Texas A&M Health Science Center and a specialist in hematologic malignancies at Scott & White Hospital, in Temple. "All of this information and even good information is available, and the way people process it is still very much humanly affected."
"This is a very complicated, 20-page article which essentially says we're all human. We cannot make risk assessments like a computer or like a professional actuary," Cable added.
The study authors noted that one way to offset biases might be to include training in medical and nursing schools and even in life-skills classes given at the high school and middle-school level.
"People get calculus and trigonometry, but they don't get the kind of stuff that is really useful to everyday life," Klein pointed out. "Today, people are making their own decisions in concert with health-care providers, and, if they're going to do that, they need to understand this. It's complicated, but it's not so complicated that the typical person who puts a little effort into it can't pick it up."
Visit Harvard University for more on disease risk.