Graphical diagnosis of interlaboratory quality control data for surface water samples

Abstract

It is shown that the ellipse offers an appropriate contour or enclosed mapping for the graphical comparison and depiction of interlaboratory quality control duplicate data. In addition, a simple method for calculating the numerical values of the major and minor axes of the ellipse is proposed. Finally, confirmatory proof is given that the bivariate regression line is coincident with the major axis of the contour ellipse, and as a consequence, the slope of the regression line is equivalent to the tangent of the angle of inclination of the major axis with the abscissa.