1. Plot of results from a linearity experiment to determine reportable range.
Plot of results from a linearity experiment to determine reportable range. Seven concentrations of analyte prepared by dilution of a high-concentration standard were tested in triplicate. Assigned values, (converted to log10) were plotted on the x axis versus measured values (converted to log10) on the y axis using Microsoft Excel. Linear regression analysis gave the equation y = x (r2 = ). A second-order polynomial trendline gave the equation y = −0.028x x − (r2 = ). A third-order polynomial trendline gave the equation y = 0.009x x x − (r2 = ). The second- and third-order polynomials are not significantly better (P > 0.05) than the linear equation, which indicates that the linear equation is the best fit for the data. The fitted regression line shows the slope to be significantly different from zero and the intercept to be not significantly different from zero. The regression coefficient of verifies the linearity throughout the range tested. The reportable range in this example translates to 30 copies/ml (LLOQ) through 3,000,000 copies/ml (ULOQ). Because of imprecision at the low end, more replicates in a precision experiment may need to be tested to adequately determine the LLOQ before accepting the reportable range.
Eileen M. Burd Clin. Microbiol. Rev. 2010; doi: /CMR