Aggregation over multiple available hazard characterisations

In some scenarios, it may be that for a given substance and effect there are multiple available hazard characterisations. This can happen, for instance, if there are two different NOAELs originating from different studies. In such cases, a single hazard characterisation should be derived from the available candidates.

A conservative approach is to choose the lowest hazard characterisation ($\mathrm{HC}$) of the available hazard characterisations. I.e.,

$$\mathrm{HC}=\underset{i=1,\dots ,n}{min}{\mathrm{HC}}_i$$

Alternatively, it is possible to aggregate the candidates into a new “average” hazard characterisation. For this, the harmonic mean, also used for obtaining central value estimates in the imputation of missing hazard characterisations, is a suitable approach.

$$\mathrm{HC}={\left(\sum _i^n\frac{1}{{\mathrm{HC}}_i}\right)}^{-1}$$