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IIIG Phosphorus Volatility Analysis Retention Versus Loss

IIIG Phosphorus Volatility Analysis Retention Versus Loss. D. Boese February 29, 2008. General. Data Taken from TMC website (IIIG P Volatility.csv) Data set includes 151 observations, 148 of which include complete information (Oil Level, Ca and P for all time periods).

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IIIG Phosphorus Volatility Analysis Retention Versus Loss

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  1. IIIG Phosphorus Volatility AnalysisRetention Versus Loss D. Boese February 29, 2008

  2. General • Data • Taken from TMC website (IIIG P Volatility.csv) • Data set includes 151 observations, 148 of which include complete information (Oil Level, Ca and P for all time periods). • Analysis consists of comparisons of precision of EOT P Loss and EOT P Retention. • P Retention (%) is a relative measure of Phosphorus volatility and P Loss (g) is an absolute measure.

  3. EOT P Retention Versus Loss Precision Analysis There are several ways to compare precision. • For each method, three sets of calculations are made based on different data subsets: • All Testkeys in Phosphorus database • All Testkeys other than 60251 which has the following Ca results for the initial through the EOT time periods, respectively: 0.2000, 0.2300, 0.2953, 0.7625, 0.2477, and 0.3205. The P Loss for this Testkey is negative. • All Testkeys excluding outliers (studentized residual greater than 3) which are 50623, 52878, 60251. The purpose of this group is to determine if deletion causes a dramatic change in the ranking of methods. • The following methods are in order of descending preference. Only the first two methods provide information regarding discrimination among oils.

  4. EOT P Retention Versus Loss Precision Analysis 1. Power curves for Oils 434 and 435. • Power (1 – β) is probability of correctly rejecting null hypothesis of equality. • It is assumed that the same number of tests are performed on each oil (number of observations). • Via Regression Analysis (all data): • P Loss: • RMSE = 0.164g • Oil 434 LS Mean = 1.13g • Oil 435 LS Mean = 0.83g • P Retention: • RMSE = 2.29% • Oil 434 LS Mean = 75.7% • Oil 435 LS Mean = 82.3% • For β = 0.1, P Loss requires 4 observations per oil whereas P Retention requires 3 observations. • Via Regression Analysis (omitting Testkey 60251): • P Loss: • RMSE = 0.129g • Oil 434 LS Mean = 1.16g • Oil 435 LS Mean = 0.83g • P Retention: • RMSE = 2.30% • Oil 434 LS Mean = 75.7% • Oil 435 LS Mean = 82.3% • The Power of P Retention is slightly higher than that of P Loss.

  5. EOT P Retention Versus Loss Precision Analysis (Continued) 1. Power curves for Oils 434 and 435 (continued). • Via Regression Analysis (omitting outliers: Testkeys 50623, 52878, and 60251) • P Loss: • RMSE = 0.108g • Oil 434 LS Mean = 1.16g • Oil 435 LS Mean = 0.83g • P Retention: • RMSE = 1.98% • Oil 434 LS Mean = 75.7% • Oil 435 LS Mean = 82.1% • For β = 0.1, both methods require 2 observations per oil.

  6. EOT P Retention Versus Loss Precision Analysis (Continued) 2. Anticipated range of results versus variability. • Assume Oil 434 at the high end of the range for volatility and no volatility at the other end of the range. • Desire Range to Variability Ratio (R/V) to be high. • Utilize RMSE as estimate for variability and Oil 434 LS Means as estimate of Oil 434 mean. • R/Vs of P Retention are slightly better than those of P Loss. 3. Number of outliers (studentized residuals with magnitude of 3 or higher): • Does not take into account ability to discriminate among oils of interest. • Utilized the regression analysis of P Loss and P Retention with Lab and Oil as predictors. • P Loss had one additional outlier (Testkey 60251 which had ahigh level of Ca at 60 hours).

  7. EOT P Retention Versus Loss Precision Analysis (Continued) 4. Coefficient of Variability (CV = Standard Deviation/Mean) • Does not take into account ability to discriminate among oils of interest. • Is the only criteria of the four that is scale dependent, i.e., if 1000 is added, or if the result is subtracted from 100 (P Ret converted to P Loss), a much different CV results though discrimination remains unchanged. • Due to the above two items, this method is not preferred. • Utilize RMSE and Mean of all Responses. • CV of P Loss compares favorably to that of P Retention.

  8. Comparison of Phosphorus Volatility and IIIG Precision (All Data) • For purposes of comparison to an existing test, precision data were calculated for the IIIG critical parameters using the same Testkeys. No outliers were excluded. • The power statistic was calculated for each of the three pairs of oils. • The power of P Retention and P Loss compare favorably to the IIIG parameters.

  9. Comparison of Phosphorus Volatility and IIIG Precision (Omitting 60251) • Precision calculations are made on all parameters omitting Testkey 60251. • The main change is that the power of the P Loss improved slightly resulting in the same number of tests (3) as for P Retention to yield a power of greater than 0.9.

  10. Conclusions • The four precision statistics considered in this analysis slightly favor EOT P Retention to EOT P Loss. • In general, either Phosphorus Volatility method provides better discrimination of reference oils than the IIIG tests. • Though the statistics slightly favors EOT P Retention, P Loss is more of a direct assessment of the amount of P being volatilized if oils with different P contents are compared.

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