PEST RISK ANALYSIS (PRA) TRAINING Group Exercises Manual

PEST RISK ANALYSIS TRAINING - GROUP EXERCISES MANUAL GROUP EXERCISE NO. 3.4
GROUP EXERCISE NO. 3.4 – PEST RISK ASSESSMENT CONCLUSIONS
At the end of Stage 2: Pest Risk Assessment, an overall assessment of risk will have
been estimated for each of the pests included in the PRA, and an endangered area will
have been defined if required. The overall assessment incorporates the elements of
probability (entry, establishment, and spread) and potential impacts (direct and
indirect, economic and environmental) which have so far been considered separately.
Based on the overall assessment, a determination of whether the estimated risk is
acceptable or not is made for each pest. For those pests, whose estimated risk is
considered acceptable, the PRA may stop. For those that present an unacceptable
risk, the PRA may continue. The estimation of overall pest risk, therefore, is a very
important final step in pest risk assessment.
ISPM No. 2 and ISPM No. 11 do not provide guidance on how to combine the
elements that have been considered in Stage 2 or how to draw conclusions regarding
the overall risk of a pest or pests. They, likewise, do not provide instructions for
determining if a specified level of risk is acceptable or not. Expert judgement
acquired through experience with PRA and consultation with others is required.
Different approaches have been taken by various NPPOs; the common feature of all
of these is their interpretation of risk as a product of likelihood and impact.
Using the information documented so far and keeping in mind this interpretation of
risk, devise a scheme for summarizing the overall risk posed by the pest in this PRA
and for determining if the level of risk is acceptable or not. You may or may not wish
to assign ratings. The summary table provided on the next page may be useful but
you may prefer to devise your own system. Keep in mind that it is also important to
document the areas of uncertainty and the degree of uncertainty in the assessment,
and to indicate where expert judgement has been used.
Questions to consider in devising your scheme:
• Are likelihood elements (entry, establishment and spread) and impact
elements (economic or environmental effects) equally important or are some
elements more important than others?
• How can quantitative and qualitative data be incorporated into a single
conclusion?
• Is consistency between risk assessments an important feature? Will my model
help to achieve that?
• How can I demonstrate how the overall conclusion was reached?
• How should the overall risk be expressed? Numerically? Descriptively?
• What considerations would influence a decision about whether or not a
specified level of risk was acceptable?
• Will my overall risk assessment conclusion provide the necessary information
to determine if the risk is acceptable, or not, as required at the end of Stage 2?
• Have I sufficiently documented my findings, sources of information and
conclusions?
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