  Agreement between measurement methods is commonly investigated by a so-called
Bland-Altman plot showing if the difference is independent of the size of the
measurement. However, such analysis assumes that both methods have the same
precision. If not, the plot may show a false trend caused by the difference in
precision and not by an actual dependence on the size of the measurement. We
suggest a modification of the Bland-Altman plot such that the differences are
plotted against an inverse-variance weighted average of the measurements rather
than their mean. This study shows that such modification removes the dependence
on difference in precision.
