Statistical determination of preservative threshold retention in soil block tests

This statistical approach allows estimation of the threshold retention value for preservatives assayed in soil block tests. The threshold value corresponds to 1% (or any other positive value) weight loss from decay only. An associated confidence interval can be given for this threshold estimate, allowing comparison of different preservatives. An "operational" weight loss line is used to adjust the percent weight loss data for loss caused by preservative or solvent evaporation. The adjusted data are then fitted by an exponential or logistic model. Statistical tests for lack of fit are used to test model assumptions. Plots are used to visually judge fitted curves and the estimated threshold preservative retention.