Lesson 7, QC Planning for Healthcare Laboratories, WesTgard ® Quality Corporation © 1997

Lesson 7: QC Planning Tools -What are Critical-Error Graphs?

This lesson on Critical-Error Graphs demonstrates the quantitative use of power function graphs by calculating the size of medically important errors, then imposing these critical-errors on the power curves to determine the probabilities for rejection. The application of critical-error graphs is illustrated by QC Selection for a Multitest Chemistry Analyzer that performs 18 different tests. A detailed application of the QC Validator program is illustrated for albumin via downloading the Multi-test Chemistry example.

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Objectives:

Learn to calculate critical-sized errors.
Understand how a critical-error graph is prepared.
Understand how to read a critical-error graph.

Web materials:

Lesson: Critical-Error Graphs
QC planning application: Multitest chemistry analyzer
QC Validator tutorial for an albumin example

Things to do:

Study the materials.
Run the QC Validator Multi-test Tutorial (example for albumin).
For a test of interest, find out the precision and accuracy observed in your laboratory. Define the quality requirement for that test and calculate the critical systematic error.
Use the QC Validator program to determine the probabilities of false rejection and error detection for that test.

Assessment: View the Answers

What is the critical systematic error when TE_a is 10%, bias_meas is 0.0%, and s_meas is 2.13%?
What is the critical random error?
What are the P_frs for 1_2s, 1_2.5s, 1_3s/2_2s/R_4s/4_1s, 1_3s, and 1_3.5s with Ns of 2 and 4?
What are the P_eds for detecting the critical SE by the same QC procedure?
What would be an appropriate QC procedure for this test?
What would be an appropriate QC procedure for the test of interest in your laboratory?

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