QC Statistics and Rules
Introduction
IMMAGE 800 Operations Manual A11403
Quality Control
September 2016
Page 9-3
9
QC Statistics and Rules
Introduction
The following section describes the QC rules used by the Quality Control feature.
Determination of QC Flags
The IMMAGE 800 uses the Z-score method for standardizing the scale of a normally
distributed measurement variable. For an individual control result, the Z-score
represents the distance in standard deviations from the assigned mean. The Z-score is
calculated from the following equation where:
Each time a control result is received, the Z-score is calculated. If the Z-score is less
than ± 2 SD, the result is within the assigned control range (the assigned mean ± 2
assigned standard deviations) and is considered acceptable.
Results are flagged at time of run. Flagging is not changed if the operator modifies the
assigned mean and/or SD.
If the operator chooses to use a QC program other than the IMMAGE 800 QC
program, assigning a mean of "0" and an SD of "99999" for a chemistry prevents
additional flagging of the results in the IMMAGE 800 QC database and on the
IMMAGE 800 screen.
Accuracy and Precision Flags
The IMMAGE 800 utilizes the following Westgard rules for evaluation of QC data.
1-2S: Result Between ± 2SD and ± 3SD From the Assigned Mean
If the result is between ± 2 and ± 3 standard deviations from the assigned mean, the
result:
- is flagged as > 2SD on the QC Log report.
- is marked with a yellow 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.
X
=
the individual control result
X
=
the assigned mean for the control
SD
=
the assigned standard deviation for the control
Z =
X - X
SD
E011375L.EPS