Precision
Precision is a measure of how well the Y value represents the X value. It is most commonly used in assay quality control (see "Geological Application" below), where X is the first assay value and Y is the matching repeat assay.
The precision value is an indication of variability in the differences between individual X-Y values, relative to the average X value. It can be expressed mathematically as:
A perfect result has a precision of zero. Values of greater than zero represent an increasing amount of deviation; for example a precision of 10% indicates that the difference between X and Y varies by around 10% of X.
Calculating Precision
Precision can be calculated using the following equations. The mean, standard deviation, and variance of the two variables are required. The Pearson Correlation Coefficient is also needed. All results must be to at least five or six decimal places to produce a useable precision figure.
The figures are applied as follows:
Where:
Where:
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= Standard Deviation |
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= Pearson Correlation Coefficient |
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= Variance |
The complete expansion is:
