QC Statistics and Rules
Flags Generated on Printed QC Reports
Quality Control
IMMAGE 800 Operations Manual A11403
Page 9-4
September 2016
1-3SD: Result Greater Than 3SD From the Assigned Mean
If the result is greater than ± 3 SD from the assigned mean, the result:
- is flagged as > 3SD on the QC Log report.
- is marked with a red warning symbol beside the value on the QC Log and QC
Chart screens.
- is highlighted in a real-time pop-up window on the monitor as the system is
running.
2-2S and R-4S: Results Between 2 SD and 3 SD as Compared to the Previous
Result
In addition, the Z-score for the current result is compared with the Z-score of the
previous result in the same QC file. If both Z-scores are beyond 2 SD on the same side
of the assigned mean, the current result receives an "Accuracy" flag on the QC Log
report; this flag signifies a violation of the 2-2S rule. These values appear with a red
warning symbol in the QC Log and QC Chart.
If the two results being compared are greater than 2 SD on opposite sides of the
assigned mean, the current result receives the "Precision" flag on the QC Log report,
signifying a violation of R-4S rule. These values appear with a red warning symbol in
the QC Log and QC Chart.
•
Results Greater Than 4 SD From the Assigned Mean
Results greater than 4 SD are included in the QC Log and QC Chart, but are not used
to calculate statistics.
Flags Generated on Printed QC Reports
These flags appear in the remarks column of the QC results report:
• Greater than 2SD.
• Greater than 3SD.
• Two successive controls greater than 2SD (Accuracy).
• Two successive controls greater than 2SD on opposite sides of the assigned mean
(Precision).
Additional QC Precision Rules
Some additional Westgard QC rules are helpful when determining whether the system
is in control. These are not flagged by the IMMAGE 800 QC program but can help in
determining system performance. (Refer to Figure 9.1.)
•
4-1S Within or Across: Last Four Results of One or Two Levels of Control
Were More than 1 SD From the Mean on the Same Side
This rule judges the result out-of-control if the last four results from one or two
levels were more than 1 SD from the mean in the same direction.