Directions for Using Normalized OPSpecs Charts to Select
a QC Procedure
- 1. Define the analytical quality requirement
for the test in the form of an allowable total error, such as
given by the CLIA PT criteria for acceptable
performance in a proficiency testing event. For example, TEa
is 10.0% for cholesterol.
-
- 2. Evaluate the imprecision and inaccuracy
of your method. To define your operating point, express your
observed imprecision and inaccuracy as a percent of the allowable
total error. For example, a 2% observed CV would be 20% of a
10.0% TEa; a 1% observed bias would be 10% of a 10.0%
TEa. You can use the Normalized OPSpecs Calculator
available below.
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- 3. Obtain Normalized OPSpecs charts, such
as those available here, for common control rules with N's of
2 and 4 for two control materials, or for common control rules
with N's of 3 and 6 for three control materials. These are available
by download or by following links on this page.
-
- 4. Plot your normalized operating point on
the Normalized OPSpecs Chart for 90% AQA
for control rules with N=2 or for 90%
AQA for control rules with N=3. For example, the cholesterol
normalized operating point would be 20% on the x-axis and 10%
on the y-axis.
- 5a. Inspect the 90% AQA chart and select
a control rule(s) whose operating limits are above your normalized
operating point. Identify the control rule(s) from the key at
the right side of the chart.
- 5b. If no QC procedure can be selected in
step 5a, try the 90% AQA & N=4 chart
or 90% AQA & N=6 chart.
- 5c. If no QC procedure can be selected in
step 5b, and if your analytical method is very stable (and only
occasionally has a problem), plot your normalized operating point
on the 50% AQA & N=4 chart or the
50% AQA & N=6 chart.
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- 6. If no QC procedure can be selected in
steps 5a-c, use a "maximum" QC procedure such as the
multirule procedure with N=4 or use
the 2 SD limits with N=2.
-
- 7. Select at Total QC strategy on the basis
of the error detection expected, as described in the Lesson
on Total QC Strategies on this website.
-
- 8. Reassess for changes in method performance.
To Recap:
For two control materials:
Try this chart first: Normalized OPSpecs
Chart for 90% AQA, N=2
Try this chart second: Normalized OPSpecs
Chart for 90% AQA, N=4
Try this chart third: Normalized OPSpecs
Chart for 50% AQA, N=4
For three control materials:
Try this chart first: Normalized
OPSpecs Chart for 90% AQA, N=3
Try this chart second: Normalized OPSpecs
Chart for 90% AQA, N=6
Try this chart third: Normalized OPSpecs
Chart for 50% AQA, N=6
To download the
Normalized OPSpecs Charts (PDF), click here
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