Table 2 Correlations of outlier values between years for each comparator and threshold. To describe the year-to-year relationships in overtreatment performance (as measured by outlier values), correlation matrices were generated. The diagonal values within each 4-by-4 threshold/comparator combination show that outlier values in adjacent years are highly correlated and that the year-to-year correlation decreases with increased separation. The lowest correlations within each threshold and comparator are generally seen between 2009 and 2013. The correlations calculated using all VA facilities and facilities of the same complexity as the comparator are very consistent; the VISN comparator correlations are generally lower

From: Identification of outliers and positive deviants for healthcare improvement: looking for high performers in hypoglycemia safety in patients with diabetes