Published on July 19, 2005 at 7:25 AM
According to a review of 49 recent major medical studies, it has been discovered that nearly a third were later either totally contradicted or were found be much less effective than was originally thought.
The studies were selected on the basis of how often they were mentioned in later medical journal articles.
Some good examples are the 1991 study which concluded that taking hormones after menopause was probably good for protecting women's hearts from coronary artery disease, but by 2002 investigations proved that the opposite was in fact true.
A small study in 1991, found that giving a patient a particular antibody could reduce the patient's risk of dying from some infections, but a later, larger trial found again that was not the case at all.
And so on - but thankfully not all studies, are likely to be contradicted.
A good example is the 1998 review found that intensively managing Type II diabetes reduced a patient's risk of complications.
According to clinical epidemiologist John Ioannidis, a professor at the University of Ioannina in Greece, in the diabetes trial, the effect was so strong that it would be unethical to test it in a randomized trial, where some patients' diabetes was less intensively controlled.
Ioannidis carried out the analysis of these studies, and his findings appear in the JAMA: The Journal of the American Medical Association.
The American Medical Association ironically also initially published many of the 49 studies he has examined.
Ioannidis says that 'science is never final', and in a few years another study could overturn his results, too!