c4 data - Chapter 4 Statistics in Analytical Chemistry 1...

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Chapter 4 Statistics in Analytical Chemistry 1
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You can’t have accuracy without good precision. But a precise result can have a determinate or systematic error. Accuracy and precision Accuracy: A measure of how close a measured value is to the “true” value. Precision: A measure of the reproducibility of a measurement. 2
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Accuracy and precision Accuracy: A measure of how close a measured value is to the “true” value. % 100 % t t t x x x Er x x Er Absolute Error Relative Error 3
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4 Normal error curve. Random errors follow a Gaussian or normal distribution. We are 95% certain that the true value falls within 2σ (infinite population), IF there is no systematic error. 4-1 Gaussian Distribution
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5 Mean Median Precision: S, RSD, CV
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9 Measurement ppm of Fe 1 19.4 2 19.5 3 19.6 4 19.8 5 20.1 6 20.3
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10
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Standard Deviation, S • standard deviation, small data set 11
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Deviation Standard Relative , x s RSD 12 Relative Standard Deviation, RSD
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Coefficient of Variation, CV 13 Variation of t Coefficien , % 100 x s CV
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4-2 Confidence Intervals 14 All measurements contain experimental error, so it is never possible to be completely certain of a result. But, “Is my red blood cell count today higher than usual?”
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15 Normal error curve. Random errors follow a Gaussian or normal distribution. We are 95% certain that the true value falls within 2σ (infinite population), IF there is no systematic error. 4-2 Confidence Intervals
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The carbohydrate content of a glycoprotein (a protein with sugars attached to it) is determined to be 12.6, 11.9, 13.0, 12.7, and 12.5 g of carbohydrate per 100 g of protein in replicate analyses. Find the 90% confidence intervals for the carbohydrate content. Uncertainty
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This note was uploaded on 04/18/2011 for the course CHEMISTRY 210 taught by Professor Dr.han during the Spring '11 term at Fayetteville State University.

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c4 data - Chapter 4 Statistics in Analytical Chemistry 1...

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