The weaker or non-existent associations are not due to fraud or poor study design, Ioannidis has cautioned. Part of the reason that small studies may not be confirmed by larger ones has to do with statistical probability, which determines the chance of a certain occurrence. To take the example of flipping coins, for example, someone may get four heads in a row in a few coin flips, but if he or she flips a coin hundreds of times, the odds of heads to tails will always approach a 50:50 ratio.
"Some biomarkers definitely work, so I think they can be very helpful. But just because one study suggests they're going to be effective, we can't just assume it will work across the board," said Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City.
"These things are very exciting when you find them," she added. "It's important for us to look for markers . . . but we have to keep a critical mind, because what at first seems like a very important finding may not pan out."
Fierce competition among scientists to report significant findings and a hopeful public eager for advances in the fight against dread diseases may add to any exaggeration of a study's importance, Ioannidis and other experts agreed.
The studies analyzed included one linking the BRCA1 mutation with colon cancer, another tying blood levels of C-reactive protein to cardiovascular disease, and one associating levels of the amino acid homocysteine with vascular disease. Researchers have also reported recent biomarker evidence in conditions such as Alzheimer's disease, leukemia and kidney disease.
The researchers reported that meta-analyses found all but a few of the association
All rights reserved