Ioannidis considered all the highly cited papers published in key medical journals during the years 1990 to 2003. Of those, 45 found that a medical intervention was effective. He then tracked all reports of these interventions’ efficacy over the years to come. He found that seven (16 percent) were later found to be ineffective, another seven (16 percent) were found less effective than initially believed, 20 (44 percent) were supported in future studies, and 11 (24 percent) were never tested again.
