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15.1 Qualitative evaluation of uncertainties

The EFSA approach starts with a systematic examination of all parts of the assessment to list all identifiable sources of uncertainty. Initially, every uncertainty is evaluated qualitatively. This could be done in various ways, but the EFSA (2006b) document suggests using scores in the form +, ++, +++, -, - -, - - - and combinations such as - / ++ to represent a subjective assessment of the direction and magnitude of the influence of each source of uncertainty on the outcome of the assessment (i.e. to indicate how different the true outcome might be). A similar score is then assigned to represent a subjective evaluation of the combined influence of all the identified uncertainties. EFSA (2006b) suggests presenting this evaluation in a tabular format: an adaptation of this format for risk-benefit assessment is illustrated in Table 2.

Table 2. Tabular approach for qualitative evaluation and expression of uncertainties affecting risk-benefit assessments (adapted from EFSA, 2006b). The +/- symbols indicate whether each source of uncertainty has the potential to make the true health impact of changing from the reference to alternative scenario more beneficial (+) or adverse (-). The number of symbols provides a subjective relative evaluation of the magnitude of the effect (e.g. +++ indicates an uncertainty that could make the true benefit much higher). If the effect is uncertain, or could vary over a range, lower and upper evaluations are given (e.g. - / ++ or + / ++). Finally, the combined impact of all the uncertainties is evaluated subjectively.

Source of uncertainty

Magnitude and direction of influence on true net health impact

Concise description of source of uncertainty

(e.g. intake of contaminant in alternative scenario may be under-estimated due to treating non-detects as zero concentrations)

Symbols to show evaluation of influence

(e.g.: -/- -)

Insert one row for each source of uncertainty affecting the assessment

 

 

 

Overall evaluation of uncertainty affecting the assessment outcome

Add narrative text here, describing the assessor’s subjective evaluation of the overall degree of uncertainty affecting the assessment outcome, taking account of all the uncertainties identified above.

 

Evaluation of overall uncertainty

(e.g. - - - / +)