That omission of key information, namely the numbers, is common to many -- perhaps most -- claims about drugs and medical interventions, regardless of the source of the claims, according to the study. It's routine in drug advertisements. It's common in announcements from many institutions that have found a dangerous side effect and want to be sure they get your attention.
But it's wrong.
There are several other ways that statistics can be very misleading, like overstating survival rates, or implying that in all cases early screening can lead to early detection and more successful treatment, the researchers contend.
In his unsuccessful attempt to win his party's nomination for president, Rudy Giuliani said in a campaign advertisement: "I had prostate cancer, 5, 6 years ago. My chance of surviving prostate cancer -- and thank God, I was cured of it -- in the United States? Eighty-two percent. My chance of surviving prostate cancer in England? Only 44 percent under socialized medicine."
That is flat out wrong, according to the researchers. "Giuliani's numbers are meaningless for making comparisons across groups of people that differ dramatically in how the diagnosis is made," the report states.
Giuliani's claim that men are nearly twice as likely to survive in the United States as in England is based on a five-year survival rate after detection. In a 2000 study, 49 British men per 100,000 were diagnosed with prostate cancer, of which 28 died within five years, about 44 percent. But screening for prostate cancer is different in England than in the United States. This country relies heavily on a prostate-specific antigens (PSA) test, which can sometimes detect cancer earlier. But the test is not widely used in England. Thus, the detection, and the five-year survival rate, spans a different time in the lives of patients in the two countries.
To illustrate the point, the report turns to a hypothetical situation:
"Imagine a group of prostate cancer patients currently diagnosed at age 67, all of whom die at age 70. Each survived only three years, so the five-year survival of this group is 0 percent. Now imagine that the same group is diagnosed with prostate cancer by PSA tests earlier, at age 60, but they all still die at age 70."
If the patients in the second group lived to the age of 65, their five-year survival rate would be 100 percent, although they all died by age 70.
"Even though the survival rate has changed dramatically, nothing has changed about the time of death," the report notes.
"Are American men half as likely to die from prostate cancer as British men are?" the study continues. "The answer is no; the risk is about the same: About 26 prostate cancer deaths per 100,000 American men versus 27 per 100,000 in Britain."
Not to worry, the doctor always knows best, right? Not necessarily, according to the report.
In several studies, physicians were asked if they really understood what the widely known 25 percent risk reduction by mammography screening really means. If 1,000 women are tested, how many fewer will die of breast cancer?
The answers were all over the map, ranging from one out of 1,000 to 750 out of 1,000. Fortunately, most gave the correct answer, the researchers say, which is one. One more survivor will be added to the list, and that's 25 percent of the total number of survivors. But even after the answer was revealed, one physician insisted it should be 250.