Comparison of sampling procedures for two rice diseases: leaf blast and tungro

The precision and accuracy of eight random and systemic sampling methods, along with various sample sizes, were compared by means of a sampling simulation program with actual field data for two rice diseases, leaf blast and tungro. Three severity levels of leaf blast and two incidence levels of tungro were used. Precision depended primarily on disease intensity, followed by the sample size and the sampling method. Relative accuracy did not prove to discriminate sampling methods adequately, but simulated absolute accuracy is able to identify biases of systematic sampling paths. The results emphasize the necessity of pilot sampling at various stages of epidemics. The usefulness of simulated sample sizes and sampling methods based on real data is also demonstrated. With this approach a more practical combination of sample size and method may be found for different levels of disease intensity using precision and absolute accuracy as criteria.