Paris - Some 18% of endurance athletes showed signs of blood doping at the 2011 and 2013 world championships, according to a report led by the University of Lausanne.
"Our results from robust haematological parameters indicate an estimation of an overall blood doping prevalence of 18% in average in endurance athletes," the report said.
The results suggested a higher proportion of female athletes (22%) than in male athletes (15%) were suspect.
The report's authors had access to blood samples from 1,222 athletes who took part in endurance events (race walking and track events from 800m) in Daegu in 2011 and Moscow in 2013.
The IAAF's introduction of the athlete biological passport in 2011, the report argues, failed to significantly lower blood doping 2013.
But it added: "The further development of the Athlete Biological Passport with a careful monitoring of biological parameters still represents the most consistent approach to thwart athletes using undetectable prohibited substances or methods."