A number (equal or greater than 1) used to divide NOAEL or LOAEL values
derived from measurements in animals or small groups of humans, in order to
estimate a NOAEL or LOAEL value for the whole human population; also called
margin-of-safety.
Uncertainty factors are used to compensate for a deficiency in knowledge
concerning the accuracy of test results and the difficulty in estimating the
health effects in a different species and/or in different exposure conditions.
As such, the value of the uncertainty factor depends on the nature of the toxic
effect, the size and type of population to be protected, and the quality of the
toxicological information, and includes scientific judgments.
Uncertainty factors are also used when deriving a tolerable daily intake (TDI)
from the most sensitive endpoint in the most relevant study (LOAEL or
NOAEL).
