Brain weight of male rat pups relative to body weight on postnatal day 56.

Ranges are standard error of the mean. One value is statistically signficant (300 mg/kg). The importance of this value is dismissed by Sumitomo (and we can infer by regulatory authorities who approved the use of pyriproxyfen in drinking water). The reason for this dismissal is that the 1000 mg/kg dosage value is not statistically significant and it is assumed that if pyriproxyfen is the cause of the low brain mass then the higher dosage level would also give a statistically significant result. Note, however, that the 1,000 mg/kg value (as well as the 100 mg/kg value) are low relative to the control and their values are not statistically different from the 300 mg/kg value. Remarkably, this failure of proper statistical reasoning appears to be the reason for regulatory approval.