Table 1.

IPCS preliminary distributions for human toxicokinetic and toxicodynamic variability.

Parameter	Median estimate across data sets of variation between 95th and 50th percentile individuals	95th percentile estimate across data sets of variation between 95th and 50th percentile individuals	Source
Toxicokinetic (TK) Variability	~2-fold	~4.5-fold	Based on variability in area under the curve from oral exposures in 37 data sets (Hattis and Lynch 2007a).
Toxicodynamic (TD) Variability	~2.5-fold	~10-fold	Based on observations of systemic, non-immune-mediated, continuous physiological parameter changes or quantal biological response in relation to internal measures of systemic exposures in 34 data sets (Hattis and Lynch 2007a).
Combined TK and TD	~3.5-fold	~14-fold	Based on Monte Carlo simulation combining the TK and TD distributions, assuming they are independent and lognormal.

Adapted from IPCS Tables 4.4 and A4.1 (WHO 2014)