RADIOMETER ABL90 FLEX - Statistical Parameters

ABL90 FLEX reference manual Appendix – Quality control
I-3
Statistical parameters
This section describes the terms and statistical parameters used in the topic
quality control:
Parameter Definition
Mean value,
X
The mean value is the average value as shown below:
n
X
X


where
X = single result

X
= the sum of single results
n =
number of single results
Standard
Deviation, SD
The standard deviation describes the distribution about
the mean value and is calculated as follows:
1n
)XX(
SD1
2




and can be illustrated on the normal distribution curve:
1 SD includes 68.3 % of the results.
2 SD includes 95.5 % of the results and is normally
used for clinical instruments.
Coefficient of
variation, CV%
Coefficient of variation expresses the variation in the
sampling results and is calculated as follows:
(%)100
X
SD
CV 
where SD = standard deviation and
X
= mean value
from lot-to-date.
CV% is used to compare the deviation from the
absolute mean value from lot-to-date and can,
therefore, be of limited use at low mean values with low
precision.