How are uncertainty factors selected

The selection of the specific uncertainty factors (now called adjustment factors) relies upon the professional judgement of the expert toxicologist and the use of guidelines that are in the toxicology literature. To a certain extent the selection of these values are subjective, but are based on the expert toxicologists review of the entire data set, their advance educational training, and their experience. The selection of uncertainty factors are not based on direct calculations or a direct reference. This is the accepted industry practice.

One of the guidelines that we commonly reference is Table 1 in  "Sargent EV, Faria E, Pfister T and Sussman RG (2013) Guidance on the Establishment of Acceptable Daily Exposure Limits (ADE) to Support Risk-Based Manufacture of Pharmaceutical products. Regulatory Toxicology and Pharmacology 65:242-250."

This table is presented below: