We deal with uncertainty every day. Which route should we take? Umbrella or not? Dessert?

But when it comes to life-or-death health care issues, many of us are frustrated with uncertainty, even when that's the best that medical science can offer us.

That was evident the past couple of weeks, when Americans were told they could scale back on breast cancer screenings and Pap smears after years of being told they needed annual tests, and then were told that a growing number of young people are at risk of dying from the complications of H1N1 swine flu, even as most doses of the swine flu vaccine have not yet arrived.

The U.S. Preventive Services Task Force started the seesaw by saying that women in their 40s no longer needed routine mammograms and that women between 50 and 75 could safely get screenings every other year instead of annually.

The Pap smear recommendations were less controversial but moved in the same direction. The American College of Obstetricians and Gynecologists said that most women could now get the cervical cancer screenings every other year as well.

And with the H1N1 flu, federal figures showed the number of confirmed cases had started to decline, but that there had been a "worrisome spike" in potentially lethal bacterial pneumonia cases hitting younger adults after they were infected with the swine flu.

So how are patients and doctors supposed to deal with this conflicting information? Is it the fault of poor communication by the experts, distorted messages or people not being able to understand complicated data?

It actually may be a little of each, several experts say.

First, they noted, the confusion caused by the breast cancer and Pap smear recommendations has different causes than the uncertainties over the swine flu.

The value of annual mammograms and Pap smears has been debated for years, and researchers have data from many long-term studies to guide their recommendations. Swine flu is new, though, and the questions of how many people it will infect, how many will die and who is most at risk are still evolving.

The recommendation to decrease the frequency of mammograms has been the most controversial of the three issues.

It was clouded from the start by unfounded accusations that the preventive services task force was simply trying to cut screening costs as part of a health care reform agenda.

"There are critics out there who have been saying the government is just trying to save money and is willing to compromise the health of women in the process, and I think that is grossly inappropriate," said Dr. Robert Martensen, director of the National Institutes of Health's Office of History.

There is no evidence that the prevention task force, which is made up of a wide variety of doctors, nurses and epidemiologists, considered financial impact in its recommendations, and its recommendations are similar to those made by other researchers long before the current health care reform debate, said Dr. Martensen, who emphasized he was speaking for himself.

The other problem, though, is that the screening guidelines lifted up uncertainties about mammograms that experts have known about for years, but that women and even their doctors rarely hear about.

Dr. Gerd Gigerenzer, director of the Max Planck Institute for Human Development in Berlin, said Friday that for every 10 mammograms that show a problem, only one is actually cancer, and yet most doctors treating women don't know that.

When he interviewed a large number of German obstetrician-gynecologists on that issue, they estimated that eight or nine of every 10 problem mammograms would prove to be a cancer.

Another reason for uncertainty is the intricacy of breast cancer itself, Dr. Martensen said.

Some women's breast cancer is extremely aggressive, and regular screening may not help save them, he said. Others have slow-growing cancers that won't kill them, and for them, screening may only heighten their anxiety without providing much benefit.

The women who get the most value from screening and treatment are those who have cancer in between those two extremes, he said, but right now, mammograms can't easily tell which cancers are benign and which ones are lethal.

And there is one other problem, said the husband-wife research team of Steven Woloshin and Lisa Schwartz at Dartmouth University. Groups like the American Cancer Society and Susan G. Komen for the Cure have been promoting annual breast cancer screening for years, and anyone who questions that may be treated as a heretic.

"We work really hard to make people afraid [of breast cancer] and to make them do the things we think are right but in the process, we don't give the more complicated and true message that these things have both benefits and harm," Dr. Schwartz said.

Dr. Wandi Bruine de Bruin, a social and decision sciences professor at Carnegie Mellon University, said she is "often asked to help communicate about things that are really complex, and sometimes I have people who want to just say to the public, 'Do this, and don't worry about the side effects,' but if you don't tell people the whole story, then they get confused because when you later change the policy, they think you're changing your mind."

In addition, Dartmouth's Dr. Schwartz said, many doctors are rated "partly on what percentage of their patients get mammograms; if we're going to judge your quality of care by what percentage of your patients get mammograms, that perpetuates the [annual screening] message to doctors."

For those who argue it's better to be safe than sorry, Dr. Woloshin noted that some studies estimate that for every woman who gets life-saving breast cancer treatment, there are 10 others who may get treatment for a cancer that would not have killed them. "The harm of screening is not false positives," he said, referring to test results that look bad but turn out to be benign. "The real harm is overdiagnosis, where you're treated for a cancer which left alone would never have done any harm."

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• What's the risk?

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The frustration some people are experiencing over the swine flu raises different issues, the researchers say.

Some are wondering why it has taken so long to produce and distribute the swine flu vaccine, especially because reports indicate that some children and young adults are getting very sick from the new flu strain.

Others are hearing that the flu has already peaked and are wondering whether it's even worth getting the new vaccine.

But Dr. Eric Toner, senior associate at the University of Pittsburgh's Center for Biosecurity, said there are good reasons to get the vaccination no matter what.

"I think the message should be that this virus is not going away. It will be with us until the next pandemic [from a different strain], and it likely will become our seasonal flu in subsequent years. Unless you know with certainty you already had the H1N1 strain of illness, you should get the vaccine."

Dr. Toner thinks some people's doubts about the swine flu vaccine are based on the fact that it is a new shot that is separate from the regular flu vaccine. But the irony is that if the swine flu virus had emerged just a couple months earlier than it did, there would have been time to include that strain in the regular flu vaccine, and the doubts about getting separate shots would never have occurred.

The other paradox: People are being told the swine flu tends to be mild, and some people don't even know they've had it -- yet there are those reports about healthy young people dying from it. Both things are true, the experts say, but in the case of children or young adults, it's important to put the risk in perspective, Dr. Toner said.

He estimated that of all the people who get swine flu, fewer than 1 percent end up in the hospital. Of those, only 5 percent die. Of that group, only a quarter are younger adults with no underlying medical weaknesses.

Once you work through all those figures, he said, it tells you that the risk of a healthy young adult dying of swine flu is about 1 in 10,000.

Dr. Gigerenzer, of the Max Planck Institute, said one reason the swine flu has caused so much anxiety is a particular quirk in human behavior: "It seems to be easy to elicit anxiety in people in situations where many people might die in a short period of time," he said, "but it's hard to elicit anxiety when people are going to die over a year or a period of years from causes like car accidents or firearms."

Even if swine flu matches the regular flu in how many people it kills -- and many scientists think it won't -- that would amount to about 36,000 deaths in America this year. The number of traffic accident deaths in the same period? About 40,000.

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