The overall variance in an analysis, s2, is the sum of the variances arising from the method, (smeth)2, and the variance due to sampling, (ssamp)2.
s2 = (smeth)2 + (ssamp)2
The blue curve in this figure shows the method’s contribution to the overall variance, s2, as a function of the relative magnitude of the standard deviation in sampling, ssamp, and the method’s standard deviation, smeth. The dashed red line shows that the method accounts for only 10% of the overall variance when ssamp = 3 × smeth. Understanding the relative importance of potential sources of indeterminate error is important when considering how to improve the overall precision of the analysis.
