3. Analysis of Split Samples by alextt

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									3. Analysis of Split Samples

Overview
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Michigan conducted split-sample experiment • Collect co-located samples • Provide a sample to two different labs for analysis MDEQ and ERG participated Only ACETALDEHYDE, BENZENE, CARBON TETRACHLORIDE, FORMALDEHYDE, and METHYLENE CHLORIDE (out of 17 pollutants) yielded enough data (at least 20 days) from both labs for quantitative comparisons.
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Data Summary
Pollutant Lab ERG ACETALDEHYDE MDEQ ERG FORMALDEHYDE MDEQ ERG BENZENE MDEQ CARBON TETRACHLORIDE ERG MDEQ ERG MDEQ 30 30 30 24 24 30 45 30 34 24 24 30 27 45 25 24 27 32 # of Days 25 # of Samples 32 Geo. Means (Geo. Std) 1.815 (1.805 ) 1.482 (2.079 ) 2.627 (1.727 ) 2.557 (1.835 ) 1.696 (1.683 ) 1.556 (1.667 ) 0.620 (1.124 ) 0.592 (1.119 ) 1.606 (3.506 ) 2.252 (2.783 ) Q1 1.09 1.03 1.61 1.87 1.09 1.01 0.57 0.55 0.61 1.06 Median 1.675 1.417 2.729 2.667 1.661 1.388 0.629 0.583 1.471 1.35 Q3 2.53 1.87 4.02 3.35 2.36 2.02 0.66 0.63 4.17 3.81

METHYLENE CHLORIDE

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Only data collected on the days when both labs reported concentration. Some data are treated as outliers and are not included in the summary and analysis: for Acetaldehyde on 4/22/01, 11/6/01, 3/30/02, and 4/8/02; for Formaldehyde on 4/22/01, 7/21/01, 11/6/01, 4/8/02, and 4/22/02; for Methylene Chloride on 3/3/02.

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Acetaldehyde Concentration, as Reported by Labs ERG and MDEQ.
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Formaldehyde Concentration, as Reported by Labs ERG and MDEQ.
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Benzene Concentration, as Reported by Labs ERG and MDEQ.
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Carbon Tetrachloride Concentration, as Reported by Labs ERG and MDEQ.
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Methylene Chloride Concentration, as Reported by Labs ERG and MDEQ.
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MDLs by Pollutant for Labs ERG and MDEQ.
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Data Analysis Approach
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Mixed effects ANOVA model to quantity:

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Systematic differences between two labs (bias) Random differences between two labs (precision) Temporal variability

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Compare amount of measurement uncertainty relative to temporal variability Notes: precision represents between-lab uncertainty only Could not directly assess within-lab uncertainty because of little to no replication from MDEQ.
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Data Analysis Results
Pollutant ACETALDEHYDE FORMALDEHYDE BENZENE CARBON TETRACHLORIDE METHYLENE CHLORIDE Bias Precision Environmental Bias/ Precision/ (ERG/MDEQ) (%CV) (%CV) Environmental (%) Temporal (%) (%) 27.3 14.75 27.51 89.46 54.32 6.9 13.1 5.2 -29.9 9.85 4.95 1.02 55.57 21.02 22.51 0.31 95.26 31.89 55.53 1645.53 44.15 47.26 22.24 328.27 64.56

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Conclusions
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Statistically significant bias between ERG and MDEQ for three pollutants: ACETALDEHYDE, BENZENE, CARBON TETRACHLORIDE. The overall mean concentration is higher for ERG in each case. For CARBON TETRACHLORIDE, environmental variability is so small that between-lab uncertainty appears large in a relative sense. For other pollutants, environmental variability is large enough that between-lab uncertainty appears less dramatic, but is still non-trivial. Uncertainty thresholds (MDLs) are similar for both labs for most VOCs, but MDEQ has higher carbonyl MDLs.
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Outlier
Pollutant ACETALDEHYDE Date 4/22/2001 Lab ERG ERG MDEQ MDEQ ERG ERG MDEQ MDEQ ERG ERG MDEQ MDEQ ERG ERG MDEQ MDEQ ERG ERG MDEQ MDEQ ERG ERG MDEQ MDEQ ERG logTransformed concentration concentration 0.044051222 -3.122402198 0.191362296 -1.653586813 228.2459935 5.430423966 . . 0.056804761 -2.868135143 0.057266588 -2.860037933 1.988192968 0.68722617 . . 0.6436984 -0.440524986 0.644625919 -0.439085101 0.03061529 -3.486255713 . . 0.098633779 -2.316341486 0.095407441 -2.349598708 1.557778005 0.44326045 . . 0.022736114 -3.78380068 0.046419567 -3.070034212 493.7516394 6.202032637 . . 6.302018665 1.840870005 . . 0.060158218 -2.810777229 . . 0.04479725 -3.10560852 DLflag <=RL >MDL >RL >RL . >RL >RL >RL . >RL >RL <=RL >MDL . >RL >RL >RL . <=RL >MDL >RL >RL . >RL . >RL . >RL

11/6/2001

3/30/2002

4/8/2002

FORMALDEHYDE

4/22/2001

7/21/2001

11/6/2001

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