Comparison of models used for the determination of odor thresholds

Several methods of data analysis used for the evaluation of odor detection thresholds have been examined through application to two samples of n-butanol. Panels of seven-ten people, working with a six level, IITRI, ternary forced choice olfactometer, were presented with initial concentrations of 99.5 and 52.1 ppm n-butanol during three trials. The ranking-plotting and ASTM E-679 methods were applied to the evaluation of discrimination-recognition thresholds of the odorous samples. It was found that single evaluations of detection or discrimination-recognition thresholds by either method were always ± 50%of the mean of six trials.The effects of successful guessing on the magnitudes of detection thresholds were examined in terms of a model based on the principle of maximum likelihood estimation of one, two and three trials of panel response. The magnitude of the discrimination threshold obtained by this method always fell between the detection and discrimination-recognition thresholds evaluated by the currently used models. The mean discrimination threshold of n-butanol for six trials was found to be 0.65 ± 0.25 ppm. It appears that the magnitude obtained from one trial with seven panel members would be sufficiently reliable for regulatory purposes when only one field sample is available, since any subsequent trials did not produce threshold values better than ± 40 % of the mean of six tests involving seven and ten panel members exposed to two different initial concentrations.