1. A method for determining the linearity of data points using a computer comprising the steps of: ascertaining an actual concentration (Y) of an analyte in a sample; measuring the sample to generate a result (X); computing with a computer, a value of Z from the following formula: Z = ∑ i = 1 N ⁢ X i 2 ⁡ ( X i - X _ ) 2 ⁢ ∑ i = 1 N ⁢ X i ⁡ ( X i - X _ ) computing with a computer, a nonlinear term (X−Z) 2 from each value of X; regressing X and (X−Z) 2 against Y with a computer, to generate test statistics having values; evaluating the values of the coefficients of X and (X−Z) 2 with a computer, to determine if the nonlinear term exceeds a threshold value to determine if nonlinearity exists.