Histograms of FE Z-scores in dialysis mortality data (SMR), stratified by facility size tertiles into (a) small, (b) medium, and (c) large facility groups. The smooth curves represent the standard normal and the empirical null distributions. (d) Histogram of facility size in patient-years. (e) Scatter plot of FE Z-scores versus facility size along with flagging thresholds based on the stratified EN (solid blue lines) and the smoothed EN (dotted black lines). The two vertical gray lines separate facilities into three groups by the tertiles of facility size. The red square in (e) is magnified in (f).