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A new Harris Poll, designed with the help of John Graham, Ph.D., Director of the Center for Risk Analysis of the Harvard School of Public Health, shows that the public tends to greatly overestimate their chances of developing many diseases and of being hurt by various types of accidents.

Among the risks which the public tends to overestimate very greatly are:

• Being seriously hurt in a car accident. The public, on average, believes that there is almost a 50% chance of this happening. In reality the chance is estimated to be, very approximately, one in twenty (or 5%).
• Prostate cancer and breast cancer. Women, on average, believe that there is more than a 40% chance of their getting breast cancer. Men rate their chances of getting prostate cancer at about the same level. In reality the chances are much lower than this, very approximately, one in ten (or 10%).

• Lung cancer. The public estimates their chances of getting lung cancer at 35%; when the real chances are less than 20% (two out of ten).
• Diabetes. The public estimate their chances of getting diabetes at 37% compared to a realistic estimate of less than 20% (two out of ten).
• Stroke. The public estimate of 45% compares with a realistic estimate of very approximately 20% (two out of ten).
• Heart attack. The public. s estimate of 50% is only slightly too high for men (whose average risk is four in ten) but significantly too high for women (whose average risk is just above one in ten).
• HIV/AIDs. While this was the "least likely" risk in the public. s mind (at 1.1 chances in ten), it is much higher than the realistic estimated risk of much less than one in twenty.

The only risk on our list which the public does not overestimate substantially is the risk of being hit by their spouse or partner. The data suggest that there are between one and two chances out of ten that this may happen. The average estimate is 1.3 chance out of ten.

Also included in the list of risks was that of being "shot or badly hurt by a stranger," even though we could not find any actuarial data on the real risk of this actually happening to people during their lifetimes. It has, in public perceptions, a mean risk of 3.1 out of ten, which seems high, and may be much higher than the true risk -- but we have no way to quantify this possible misperception.

In reviewing these results, John Graham, Ph.D. notes "Americans are living longer and healthier lives than ever before. Yet many people greatly overestimate their chances of being hurt or killed by many diseases and trauma. In part this may reflect the intuitive problems that people have understanding probabilities. It may also reflect the fact that there are powerful interests in society who benefit from efforts to frighten people. Furthermore, the media has a tendency to focus on all the bad things that could happen to people."

"This overestimation of risk may have both positive and negative consequences. On the one hand, people are more likely to take appropriate tests, or change their lifestyles, if they are concerned about the risks of developing cancer, heart disease or stroke. On the other hand, the overestimation of risk can trigger unreasonable demands for expensive policies which are not cost-effective."

"Although people tend to exaggerate risks, their instincts about relative risks are not too bad. People realize that heart attacks are more frequent than breast cancer and prostate cancer, and that injuries from serious car crashes are more frequent than injuries from violence committed by a stranger."

"I would like to ask you about various diseases and accidents. For each one, please tell me what you think are the chances of it happening to you, where ten (10) out of ten means it is certain to happen, zero (0) out of ten means no chance at all.

How many chances out of ten do you think there are that you will ever (READ LIST)?"

"I would like to ask you about various diseases and accidents. For each one, please tell me what you think are the chances of it happening to you, where ten (10) out of ten (10) means it is certain to happen, zero (0) out of ten (10) means no chance at all.

How many chances out of ten do you think there are that you will ever (READ LIST)?"

"I would like to ask you about various diseases and accidents. For each one, please tell me what you think are the chances of it happening to you, where ten (10) out of ten (10) means it is certain to happen, zero (0) out of ten (10) means no chance at all.

How many chances out of ten do you think there are that you will ever (READ LIST)?"

This Harris Poll was conducted by telephone within the United States between October 14 to 20, among a nationwide cross section of 1,013 adults. Figures for age, sex, race, education, number of adults and number of voice/telephone lines in the household were weighted where necessary to bring them into line with their actual proportions in the population.

In theory, with a sample of this size, one can say with 95 percent certainty that the results have a statistical precision of plus or minus 3 percentage points of what they would be if the entire adult population had been polled with complete accuracy. Unfortunately, there are several other possible sources of error in all polls or surveys that are probably more serious than theoretical calculations of sampling error. They include refusals to be interviewed (non-response), question wording and question order, interviewer bias, weighting by demographic control data and screening (e.g., for likely voters). It is difficult or impossible to quantify the errors that may result from these factors.

These statements conform to the principles of disclosure of the National Council on Public Polls.

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