Tools, Technologies and Training for Healthcare Laboratories


QC Selection Grid, Square 4


This is not a good situation because you have a moderate number of problems and medically important errors are small and difficult to detect. You should use a five rule procedure with N=4. The 8x rule should be used across runs and interpreted as a rejection rule. 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.