Intra species factors

Intra-species factors describe variation between individuals concerning their individual sensitivities to experience well-defined health effects. Traditionally the intraspecies factor is a fixed value, but the true distribution might be (very) uncertain. There is some support for assuming a lognormal distribution to describe the variability between individuals. In MCRA, intraspecies factors are sampled from a lognormal distribution, characterised by a geometric mean (GM) equal to 1 and a geometric standard deviation (GSD) thats needs to be given a value representing the intraspecies variability. GM is 1 by definition (50% of the population is assumed to be less sensitive than the average, 50% is mor sensitive) and has no uncertainty. On the other hand, there is uncertainty about the GSD. In MCRA it is assumed that this uncertainty is described by a Chi-square distribution with df degrees of freedom. By specifying a lower and upper bound for the p95 sensitive individual e.g. a lower value 2 and upper value 10 (meaning, the p95 individuals are between 2 and 10 times more sensible than the average human), a Chi-square distribution can be estimated where 1) the GSD specifies the variability and 2) the degrees of freedom specifies the uncertainty around the GSD.

This module has as primary entities: Substances Effects

Output of this module is used by: Hazard characterisations

Intra species factors as data

In the simplest approach, intra-species factors are fixed factors. In a higher tier, lower and upper values for the intra-species factor are used to derive a variability distribution (log-normal around 1) and an uncertainty distribution for the geometric standard deviation related to human variability in sensitivity.

Inputs used: Active substances

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