If you were told a drug you are taking has been found to increase the risks of death by 100 percent, would you stop taking it? Of course. But does that statement really mean you are much more likely to die if you keep taking the drug? Absolutely not.
Statistics like that, touting drugs and their possible side effects, can be so misleading that even doctors frequently misunderstand them, according to a major international study that brands many health care professionals as "statistical illiterates."
The report, published in the current issue of Psychological Science in the Public Interest, cites numerous instances of grossly overstated benefits, or adverse effects, of drugs and medical procedures, which, in some cases, has had devastating results.
The researchers accuse drug companies of knowingly using misleading statistics to promote their products because a "big number" can lead to a big headline and lots of sales. And a well-meaning institution might also seek a big number to warn of possible dangerous side effects of a drug, even if that number implies a much greater risk than actually exists.
Statistical skullduggery strikes at just about every level, from professional medical journals to health care workers to medical writers who convey the bad numbers that frequently come from news releases promulgated by some of the leading research institutions in the world, the report says.
"Many doctors, patients, journalists, and politicians alike do not understand what health statistics mean," according to the study, authored by two medical professors at Dartmouth Medical School, Steven Woloshin and Lisa M. Schwartz, and their collaborators, psychologists Gerd Gigerenzer, Wolfgang Gaissmaier and Elke Kurz-Milcke of the Max Planck Institute for Human Development in Berlin.
One of many cases they cite had tragic consequences. In 1995, the United Kingdom Committee on Safety of Medicines issued a warning that "third-generation oral contraceptive pills increased the risk of potentially life-threatening blood clots in the legs or lungs twofold -- that is, by 100 percent," the report states. It was a big number, and it got a lot of attention, but it was very misleading.
"This information was passed on in 'Dear Doctor' letters to 190,000 general practitioners, pharmacists, and directors of public health and was presented in an emergency announcement to the media," the report continues. "The news caused great anxiety, and distressed women stopped taking the pill, which led to unwanted pregnancies and abortions."
The scare was blamed for 13,000 abortions the following year, many involving teen pregnancies.
But who can argue with 100 percent? The report adds:
"The studies on which the warning was based had shown that, of every 7,000 women who took the earlier, second-generation oral contraceptive pills, about one had a thrombosis; this number increased to two among women who took third-generation pills. The absolute risk increase was only one in 7,000, whereas the relative increase (among women who developed blood clots) was indeed 100 percent."
That's right. An increase from one to two, but that's out of 7,000.