QC Selection Grid, Square 8
You have few problems, but medically important errors are moderate in size, which means you should use at least three rules that can be applied to the two control measurements in a run (N=2) to improve error detection. You can also add a warning rule that works across two runs (R=2). The power curves below show the rejection characteristics within a run (R=1) and across two runs (R=2):
Plot your critical-error on the x-axis of this power function graph. Draw a vertical line from that point to intersect the power curves. Where the curves and critical-error meet indicates how much error detection each control rule will provide.