To identify factors affecting olfactometry panel performance in the measurement of environmental odours, a data bank of odour threshold measurements including 923 individual panel tests on environmental odours and 145 tests on standards were analysed statistically. There is an evident decrease in olfactory sensitivity to environmental odours with age. The group threshold tends to be one step lower for a 25 year increase in average age of panel members for Type I odours (piggery, feedlot, landfill and mushroom composting) and for 36 years increase for Type II odours (sewage and industrial coke works). The threshold for N-butanol tends to be 1 step lower for an increase of 15 years in age. People who are over 40 years old exhibited a greater variation than younger people. Although there was a minor gender difference in the sensitivity to butanol standard, it was not statistically significant (mean natural logarithm butanol threshold was 3.65 for males and 3.84 for females). Similar minor differences were exhibited in Confidence Index (CI), 1.72 for females (std. dev. 0.73) and 1.81 for males (std. dev. 0.77). Using “guess and correct” as criterion to determine individual thresholds in the forced choice olfactometry, the mean natural logarithm of ppb butanol is 1.365 lower than that for “certain and correct”. The standard deviation for “guess” and “certain” criteria were 1.093 and 0.911 respectively. The “certainty” criterion gave a better repeatability than the “guess” criterion.