1. A method for determining the linearity of data points comprising the steps of: ascertaining an actual concentration (Y) of a sample of an analyte; measuring the sample to generate a result (X); computing a value of Z from the following formula: 7 Z = &Sum; i = 1 N &it; X i 2 &af; ( X i - X _ ) 2 &it; &Sum; i = 1 N &it; X i &af; ( X i - X _ ) computing a new variable (X−Z) 2 from each value of X; regressing X and (X−Z) 2 against y to generate coefficients having t-values; evaluating the t values of the coefficients of X and (X−Z) 2, to determine if the linear term exceeds a threshold value to determine if nonlinearity exists.