Processing factors fixed or distribution based

Processing factors can be specified as fixed factors (nominal) or as statistical distributions for the variability across samples.

Variability distribution parameters are specified indirectly via the 50th and 95th percentile. Uncertainty for processing factors can be specified using uncertainty distributions of the same form as for variability. Uncertainty distribution parameters are specified indirectly via the 95th uncertainty percentiles on the 50th and 95th variability distribution percentiles.

For distribution based processing factors specify fk,nominal and fk,upper (Nominal and Upper in table ProcessingFactors). Two situations are distinguished depending on the type of transformation.

Nonnegative processing factors

Equate the logarithms of fk,nominal and fk,upper to the mean and the 95% one-sided upper confidence limit of a normal distribution. This normal distribution is specified by a mean

ln(fk,nominal)

and a standard deviation

ln(f_{k,upper}) – ln(f_{k,nominal})/1.645

Processing factors between 0 and 1

Equate the logits of f_{k,nominal} and f_{k,upper} to the mean and the 95% one-sided upper confidence limit of a normal distribution. This normal distribution is specified by a mean

logit(f_{k,nominal})

and a standard deviation

logit(f_{k,upper}) – logit(f_{k,nominal})/1.645.

See also processing correction