INVESTIGATIONS OF THE PROBLEMS OF ASSESSING AFLATOXIN LEVELS IN PEANUTS

In this study, a number of probability distributions that have been us ed to model the occurrence of aflatoxin in peanuts are compared. Two d istributions, the compound gamma and the negative binomial, are shown to have special appeal in that both can be justified by reasoning from the fundamental biological and stochastic processes that generate the aflatoxin. Since method of moments and maximum likelihood give consis tent estimates of parameters in both models, practical considerations suggest using the former. One hundred twenty datasets, each consisting of fifty observations, were not sufficient to provide goodness-of-fit tests to establish either as superior to the other as a model. Both m odels fit the data well, appreciably better than other models examined . An attractive aspect of the compound gamma and the negative binomial distributions is that, as a consequence of their theoretical underpin nings, both involve parameters that have meaningful interpretations. I n the compound gamma, the alpha parameter reflects the shape of the ke rnel-to-kernel aflatoxin content distribution, the lambda parameter re flects the number (or frequency) of contaminated kernels in the sample , and the beta parameter is a scale parameter. In the negative binomia l, the two parameters can be used as measures of mean or location and shape.