Seth Mnookin explains:
Because it’s sexier to discover something than to show there’s nothing to be discovered, high-impact journals show a marked preference for "initial studies" as opposed to disconfirmations. Unfortunately, as anyone who has ever worked in a research lab knows, initial observations are almost inevitably refuted or heavily attenuated by future studies — and that data tends to get printed in less prestigious journals. Newspapers, meanwhile, give lots of attention to those first, eye-catching results while spilling very little (if any) ink on the ongoing research that shows why people shouldn’t have gotten all hot and bothered in the first place. (I have a high degree of confidence that the same phenomenon occurs regardless of the medium, but the PLOS ONE study only examined print newspapers.) The result? "[A]n almost complete amnesia in the newspaper coverage of biomedical findings."
The Dish 