1. A method for evaluating a sample comprising: using an analytical instrument selected from the group consisting of chromatography, spectroscopy, flowmeters and balances to measure a physical property of the sample; correlating the physical property measured using the analytical instrument with results obtained from analyzing standards having known properties under similar conditions; periodically determining whether biases are present in the analytical instrument; and recalibrating the analytical instrument and reanalyzing the sample if biases are determined; wherein the step of determining whether biases are present comprises: (a) obtaining a set of multivariate data generated by the analytical instrument; (b) performing a Fourier Transform for the data in step (a) thereby generating a spectrum which indicates the frequency characteristics of the data; (c) obtaining a series of random number sets having a similar number of elements to the set of multivariate data obtained in step (a); (d) performing a Fourier Transform for each of the random number sets in step (c) thereby generating a series of spectra which indicate the frequency characteristics of the random number sets; and (e) identifying biases in the instrument whenever the Fourier Transforms obtained in step (b) are not within the expected range of random distributions given the Fourier Transforms obtained in step (d).