Quality Control Statistics Laboratory Operations Review 48
TERM EXPLANATION
Measures of dispersion
Range
Mean
Standard deviation (SD)
Coefficient of variation (CV)
Statistical parameters describing spread of data about mean, e.g., standard deviation,
coefficient of variation, range. Measurements of precision.
Difference between highest & lowest values in data set.
Sum of all observations divided by number of observations. Average of all observations.
Statistical expression of dispersion of values around mean. Requires a minimum of
20 values.
SD = where S= sum, x = individual value, x–= mean, n = number of values
Expresses standard deviation as percentage. CV % = (SD ÷ mean) × 100. The ↓the CV,
the ↑the precision.
∑( x x)
n1
-
2
^
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