 estimates were made of the proportion of chemicals that were carcinogenic , anticarcinogenic , or either in 397 long - term bioassays conducted by the national toxicology program ( ntp ) . 
 the estimates were obtained from the global pattern of p - values obtained from statistical tests applied to individual experiments . 
 these tests accounted for multiple comparisons using a randomization procedure and were found to operate at the correct level of significance . 
 representative estimates of the proportion of carcinogens [ with 90% confidence intervals ( ci ) ] compared to the ntp estimates were as follows : male mice , 0.32 ( ci , 0.19 - 0.44 ) , ntp = 0.29 ; female mice , 0 . 
 28 ( ci , 0.15 - 0.41 ) , ntp = 0.34 ; male rats , 0.35 ( ci , 0.23 - 0.47 ) , ntp = 0.36 ; female rats , 0.34 ( ci , 0.21 - 0.46 ) , ntp = 0.28 ; all sexes and species , 0.59 ( ci , 0.49 - 0.69 ) , ntp = 0.51 . 
 representative estimates of the proportion of anticarcinogens were as follows : male mice , 0 . 
 34 ; female mice , 0.27 ; male rats , 0.40 ; female rats , 0.44 ; all sexes and species , 0.66 . 
 thus , there was as much or more evidence in this study for anticarcinogenesis as carcinogenesis . 
 even though the estimators used were negatively biased , it was estimated that 85% of the chemicals were either carcinogenic or anticarcinogenic at some site in some sex - species group . 
 this suggests that most chemicals given at high enough doses will cause some sort of perturbation in tumor rates.imagesfigure 1figure 2figure 3figure 4figure 5 
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