Consistency plots: a simple graphical tool for investigating agreement in key comparisons

Abstract

A simple graphical display is described for investigating agreement among interlaboratory data with reported uncertainties. The plot consists of a measure of agreement—the significance level of a test for significant pairwise difference, adjusted for multiple comparisons—plotted as an image in which significance is represented by colour or intensity. This provides an easily interpretable graphical presentation in which the degree of consensus can be judged and in which anomalies are easily visible. The construction of the plot is discussed, with attention to the choice of adjustment for the size of the data set in checking for anomalies. The advantage over visual inspection using error bars is discussed, and some examples from metrology comparisons are presented.