Testing shelled corn for aflatoxin, Part II: Modeling the observed distribution of aflatoxin test results

The suitability of several theoretical distributions to predict the observe d distribution of aflatoxin test results in shelled corn was investigated. Fifteen positively skewed theoretical distributions were each fitted to 18 empirical distributions of aflatoxin test results for shelled corn. The com pound gamma distribution was selected to model aflatoxin test results for s helled corn. The method of moments technique was chosen to estimate the par ameters of the compound gamma distribution. Mathematical expressions were d eveloped to calculate the parameters of the compound gamma distribution for any lot aflatoxin concentration and test procedure. Observed acceptance pr obabilities were compared to operating characteristic curves predicted from the compound gamma distribution, and all 18 observed acceptance probabilit ies were found to lie within a 95% confidence band. The parameters of compo und gamma were used to calculate the fraction of aflatoxin-contaminated ker nels in contaminated lots. At 20 ppb, it was estimated that about 6 in 10 0 00 kernels are contaminated.