Inspection sampling calculator
Market access arrangements often include a requirement to inspect a sample of fruit to check for pests of concern to the importing market. Most commonly this involves an inspection of 600 pieces of post-graded fruit. If pests of concern are detected, the consignment is ‘rejected’ – or excluded from trade to that market.
A number of factors can influence whether an inspection process will reliably detect pests in consignments for trade.
The International Plant Protection Convention provides a statistical methodology for calculating the likelihood of detecting infested fruit at different sampling rates and detection likelihoods (ISPM31). For example, inspecting 600 pieces of fruit results in a 95% chance of detecting infested fruit if the infestation rates is 0.5% (1 in 200 fruit) and an infested fruit is always correctly classified. The standard includes look-up tables to guide the correct sampling rate for common scenarios.
We have developed a sampling calculator that makes the ISPM31 look-up tables easier to navigate. It also allows users to explore their own scenarios. Further, the tool extends the statistics to allow quantitative evaluation of:
- high-risk fruit inspections (such as from the reject bin)
- crop inspection in the field
Inspection of high-risk fruit is much more sensitive than inspected packed fruit. Conducting multiple crop inspections also increases the likelihood of detecting infested fruit, especially if high risk (such as damaged or early-maturing) fruit is targeted for inspection. Ongoing research will help to further refine the statistics supporting crop inspection.
For further guidance, see the ISPM 31 methodology document here:
https://www.ippc.int/en/publications/83473/
And the ISPM 31 explanatory document is here: