The tool is developed as an addition to the WHO-IPCS tool APROBA, which is a part of the guidance on “Evaluating and expressing uncertainty in hazard assessment” (2017). APROBA can do probabilistic calculations in an approximate but quick and easy way assuming that the uncertainties in the different aspects of the hazard characterization (such as Point of Departure, inter-, and intraspecies extrapolation) are lognormally distributed. This results in a probabilistic health-based guidance value rather than the usual deterministic point estimate (such as RfD, ADI). In the extended APROBA-plus, exposure estimates with an uncertainty range can be included to create a single plot, which visualizes the uncertainties in exposure and hazard.

By making the uncertainties visible, the outcome from a risk assessment becomes more transparent and informative than the more usual deterministic approaches, so that risk managers can make better informed decisions, e.g. directly taking measures or asking for refinement of the risk assessment. If the latter, APROBA-Plus can help in showing which aspects in the risk assessment contributed most to the overall uncertainty, as an indication what type of refinement would be most effective.