| Factor Application and Multiplication Approach |
| Description: specific default values are assigned for preselected areas of uncertainty. The composite UF is calculated as the product of the default values that are pertinent to the specific data sets being evaluated. Rules for modifying the resulting composite UF may be specified to address overlapping uncertainties. |
| Advantages: |
| • Transparency in OEL calculation improves user ability to interpret the OEL and its uncertainties and supports worker risk communication |
| • Relative impact of different uncertainties on the OEL are clear, allowing for a determination of the value or impact of collecting new data to relieve uncertainty |
| Disadvantages: |
| • Rigorous application of default values limits the value offered through the use of expert scientific judgment |
| • Multiplying default values may yield a composite UF which does not align with the totality of the data set, often requiring significant effort and potential user confusion in explaining departures from pre-assigned defaults |
| Uncertainty Weight of Evidence Approach |
| Description: areas of uncertainty are considered in an integrated approach, with particular focus on potential overlapping considerations and the optimum protective composite UF derived when balancing the data from all lines of evidence. |
| Advantages: |
| • Provides greater flexibility in deriving the composite UF that takes into account all aspects of the available data using a weight of evidence approach |
| • Avoids pitfalls of setting OELs that are not appropriate that can result from misapplication of default UF values or overlapping areas of uncertainty |
| Disadvantages: |
| • Absence of specific defaults limits transparency in the basis for the OEL, with resulting limitations for user communication and data collection |
| • Requires a high degree of scientific expertise in OEL development, because the approach is less prescriptive |
