# QC Selection Grid, square 9

Multirule Choice:

Very cost-effective operation is possible because you have a very stable method and the medically important errors are large and easy to detect. You can actually use a single 13s rule with N=2 for rejection. If you want to look at data over two runs, you can add a 41s warning rule to alert analysts to prospectively check the method before the next run. The power curve below shows the rejection characteristics:

Plot your critical-error on the x-axis of this power function graph. Draw a vertical line from that point to intersect the power curve. Where the curve and critical-error meet indicates how much error detection each control rule will provide.