Lesson 3: Evaluating and Selecting Options
Topic 1: Evaluate Efficacy of Measures
After reviewing the effect of industry practices and identifying possible measures for reducing or managing risk, the next step is to evaluate each potential option. This topic looks at the first of three important factors in evaluating a phytosanitary measure:
- Efficacy
- Feasibility
- Potential impacts
Objective:
- Learn how to evaluate a phytosanitary measure’s efficacy.
Evaluating measures may seem straightforward, but it is often complicated. There are many ways to reduce the risk associated with a new pest. Recall from earlier modules that risk is made up of two parts: the likelihood of a hazard occurring, and the impacts if the hazard occurs. In the case of exotic plant pests, risk management options can reduce risk by any of these means:
- Lower the likelihood that a new pest will enter the country.
- Lower the likelihood that the pest will become established in the country.
- Reduce the consequences associated with the pest introduction.
To compare the efficacy of different measures, you must indicate the desired outcome of all options under consideration with a common term of expression (a simple description of what you want to happen that applies to all the options). This can be difficult when the options you are considering have different endpoints and different methods for measuring outcomes. For example, the efficacy of a disinfestation treatment, such as hot water treatment or fumigation, is measured by level of mortality, but the efficacy of a pesticide treatment is measured by reduction in the number of pests caught in traps or found in a certain sample size of cut fruit. The efficacy of irradiation treatment is measured by the percentage of sterile individuals.
Comparing the efficacy of mitigations with the efficacy of safeguards or processes, which are themselves very difficult to measure and quantify, can be even more complicated. So can comparing the efficacy of a single measure with the efficacy of a combination of measures used in a systems approach.
Despite the difficulty, expressing efficacy in terms of a common endpoint is crucial when comparing various options. Remember, when you are looking at efficacy, what you are really concerned with is how many viable pests will survive and remain in the pathway. In other words, it is the pests that survive, reproduce, and remain on the commodity after measures are applied that pose risk. When comparing options with different endpoints, you must consider the entire pathway of introduction. Then express efficacy in terms of how each option reduces risk along the pathway. For example:
- Prevalence of viable pests in a consignment
- Proportion of viable pests removed from the pathway
- Frequency of entry (the number of pests entering per unit of time) or probability of entry (probability of pest entry per unit of commodity imported)
- Frequency or probability of establishment
- Frequency or probability of pest outbreaks
The following hypothetical scenario illustrates how to compare the efficacy of different options.
Because the identified options have different endpoints, you must find a common term (simple description) expressing the desired outcome for all the options. Then you can compare the efficacy of the various phytosanitary measure options.
You decide to express your desired outcome as: “the percentage of viable pests removed from the pathway of introduction”. The expected efficacy of each type of measure, based on available scientific and technical information, is as follows:
|
Phytosanitary Measure |
Efficacy by Percentage of Viable Pests Removed from the Pathway of Introduction |
|---|---|
|
In-transit cold treatment |
85% |
|
Packinghouse culling |
80% |
|
Irradiation |
99% |
|
Certified field management practices |
75% |
|
Early harvest (fruit not yet ripe) |
55% |
|
Methyl bromide fumigation |
90% |
|
Production in an area of low pest prevalence |
70% |
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