1. The term "probabilistic" has been used for a wide range of approaches, many of which require significantly more data than current deterministic approaches. Some probabilistic methods are specifically designed for use when data are limited, but their usefulness for regulatory assessment of pesticides has not been evaluated.


  2. The perceived strengths and weaknesses of probabilistic methods may be summarised as follows (for details see Section 4 of full report):

    Strengths and opportunities Weaknesses and threats
    • Can quantify variability and uncertainty (but not completely)
    • Can produce outputs with more ecological meaning, e.g. probability and magnitude of effects
    • Make better use of the available data
    • Can identify which factors have most influence on risk
    • May provide an alternative to field testing, or help to focus it on key uncertainties
    • Should promote better science
    • More complex
    • Some methods require more data
    • May be difficult to communicate
    • Risk of misleading results
    • No agreement on what outputs are required, or how to interpret them
    • Validation is difficult


  3. The workshop identified many areas of pesticide risk assessment where probabilistic methods could help to quantify the impact of variability and uncertainty. The workshop also identified actions that could be taken to reduce or avoid the perceived weaknesses and threats associated with using probabilistic methods.


  4. The workshop therefore concluded that probabilistic methods would improve the environmental evaluation of plant protection products under Directive 91/414/EEC, provided they were implemented appropriately to minimise their potential disadvantages. This conclusion applies to all three areas considered by the workshop: aquatic organisms, terrestrial vertebrates, and terrestrial invertebrates and plants.


  5. The workshop identified a large variety of actions that are required for the successful implementation of probabilistic methods. These actions involve a combination of novel, collaborative research and consultation with stakeholders.
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