Odour Threshold Investigation 2012 - Bay of Plenty Regional Council

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Figure 6 Between session trends in log scale. Comparing geometric means of threshold for two locations Here are “average” summaries for the untransformed threshold data for the two locations. statistic Rotorua Whakatane mean 1.83 0.89 median 1.44 0.57 geometric mean 1.44 0.62 If we log the data, find the mean and then back-transform to the original scale we get the geometric mean. We can conclude that, for skewed data of the shape we have, the geometric mean is approximately equal to the median of the data. Figure 7 with the Whakatane per-panellist data illustrates the point. 66 Environmental Publication 2012/06–A review of odour properties of H 2 S Odour Threshold Investigation 2012
14 Histogram of MnH2S_Whakatāne 12 10 Frequency 8 6 4 2 0 0 MED GMEAN MEAN 1 2 MnH2S_Whakatāne 3 4 Figure 7 Distribution of Whakatāne thresholds. We now (finally) give the results of useful analyses comparing locations which show the clear difference in average thresholds between the locations. Although our full analysis used data with all results per session per panellist, it is sufficient to simply compare the log thresholds at the two locations using a two-sample t-test. The test is justified by the approximate normality of the logged form of the data. And given that there are only two locations it is also simple to allow the variability at the locations to be different. Two-sample T for log10MnH 2 S Location N Mean StDev SE Mean Rotorua 29 0.159 0.291 0.054 Whakatāne 30 -0.208 0.362 0.066 Difference = mu (Rotorua) - mu (Whakatāne). Estimate for difference: 0.3671. 95% CI for difference: (0.1960, 0.5381). T-Test of difference = 0 (vs not =): T-Value = 4.30 P-Value < 0.0005 DF = 55. We have shown there is very strong evidence that the geometric mean thresholds at Rotorua are higher than at Whakatane. Our point estimate of the difference in the log scale is 0.3671 which corresponds to a ratio in geometric means of 10 0.367 = 2.3. We are 95% sure that the ratio is somewhere between 10 .196 and 10 .538 i.e. between 1.6 and 3.5. Note that the estimated geometric means are 10 -.208 =0.62 and 10 .159 = 1.44 as listed previously. Estimating other useful characteristics of the threshold distributions As an alternative to using transformations, some statistical software offers alternative approaches to leaving the data in the untransformed state and estimating various percentiles (such as the median), the mean, and also the proportion of the data in various data ranges. The results below used such a procedure and included fitting the threshold data with a threeparameter lognormal distribution (equivalent to the data transformation Y = log e (threshold – 0.16)). Environmental Publication 2012/06–A review of odour properties of H 2 S Odour Threshold Investigation 2012 67
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A review of odour properties of H 2
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Acknowledgements Dr Bruce Graham fo
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In relation to the second question
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6.5 Equipment 29 6.6 Requirements o
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Figure 7.10 Graphical summary of th
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The standardisation of DDO in Austr
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Figure 2.1 Odorant receptors and th
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Figure 2.3 Relative slope of odour
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Part 3: H 2 S health effects The pr
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such as composting can provide very
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Seigel et al 32 undertook measureme
Page 28 and 29: Rotorua District Council also under
Page 30 and 31: Kevern 56 undertook several surveys
Page 33 and 34: Part 5: H 2 S threshold information
Page 35 and 36: The American Industrial Hygiene Ass
Page 37: Earlier summaries of data in relati
Page 40 and 41: The results generated by the olfact
Page 42 and 43: At each round of the testing proces
Page 44 and 45: 6.7.2 n-Butanol vapour The standard
Page 46 and 47: 7.1.2 Ambient H 2 S levels No H 2 S
Page 48 and 49: Residence time for Rotorua panellis
Page 50 and 51: Figure 7.7 Example of incomplete ro
Page 52 and 53: A display of the “round” values
Page 54 and 55: Figure 7.11 Log 10 mean session dat
Page 56 and 57: Panellist means Figure 7.12 t-test
Page 58 and 59: The original concept behind the tes
Page 60 and 61: Figure 7.16 Frequency plots - perce
Page 62 and 63: Figure 7.17 Scatterplot showing n-b
Page 64 and 65: Several types of analysis of the gr
Page 66 and 67: Figure 8.1 Updated H 2 S threshold
Page 69: Appendix 1 - Olfactometer calibrati
Page 73 and 74: Appendix 3 - Dr Ray Littler analysi
Page 75 and 76: Effect of elevated ambient H 2 S On
Page 77: Figure 4 Untransformed is non-norma
Page 81: Histogram of Mn butanol Lognormal R
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Odour Threshold Investigation 2012 - Bay of Plenty Regional Council

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