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Westgard QC, 7614 Gray Fox Trail, Madison, WI 53717
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· Linear-data plotter can be used with data from a linearity experiment to assess the reportable range of a method. It provides a plot of the average of a group of replicate test results on the y-axis versus the assigned value (in % or concentration units) on the x-axis.
· SD Calculator can be with data from a replication experiment to calculate the mean, standard deviation (SD or smeas), and coefficient of variation (CV). A histogram display of the data is also available.
· Paired-data Calculator can be used with data from a comparison of methods experiment to calculate linear regression statistics (slope, y-intercept, and standard deviation about the regression line, sy/x), and the correlation coefficient (r, Pearson product moment correlation coefficient); t-test statistics (average difference between two methods or biasmeas; SDdiff, standard deviation of the differences between the two methods). It can also be used to provide a "comparison plot" that shows the test method results on the y-axis versus the comparative method results on the x-axis, as well as a "difference plot" that displays the difference between the test minus comparative results on the y-axis versus the comparative method result on the x-axis.
· Method Decision Calculator can be used to display the imprecision (%CV) and inaccuracy (%bias) of a method on a "method decision chart" to assess whether the performance of a method is excellent, good, marginal, or poor. The results from the SD Calculator and the Pair-data Calculator provide the estimates of method imprecision and inaccuracy, which are compared to the allowable imprecision and allowable inaccuracy as calculated from a defined analytical quality requirement, such as the CLIA proficiency testing criteria for acceptability.