Sampling grain shipments to detect genetically modified seed

Using the binomial distribution, the effect of sample size on the variabili ty among sample test results when sampling a lot with 1.0% genetically modi fied (GM) or biotech seed was evaluated. The coefficient of variation, cv, among 500-seed sample test results taken from a lot with truly 1.0% was com puted to be 44.5%. Increasing sample size to 1000 seeds reduced the cv amon g sample test results to 31.5%. The effects of sample size and accept/rejec t limits on the buyer's risk (bad lots accepted) and the seller's risk (goo d lots rejected) was also evaluated assuming a tolerance of 1.0% GM seed. I ncreasing sample size decreases both the buyer's and seller's risks at the same time. Using an accept/reject limit below the regulatory tolerance decr eases the buyer's risk, but increases the seller's risk. Using an accept/re ject limit above the regulatory tolerance decreases the seller's risk but i ncreases the buyer's risk.