Accuracy (trueness and precision) of a measurement or test method is to be determined with a series of test results reported by a number of participating laboratories organised by a project management.
Samples of a certain material or product are sent from a central point to a number of laboratories at different places.
- the samples shall be identical when sent out to the laboratories
- the samples shall remain identical during transport and between measurements
When estimating accuracy, it is useful to assume that each measurement result, y, is the sum of three components:
y = m + b + e
where, for a certain test object:
m is the accepted reference (or “true”) value
b is the bias
e is the random error in each measurement
The bias, b, of a laboratory
is estimated as
The bias, B, in the measurement method
where u ref the accepted reference (or “true”) value.
The variance in the measurement result, Var(y), is thus the sum of the variances in the bias and the error.
The variance in the bias between laboratories
Var(b) = sL2
The variance in the error for each laboratory:
Var(e) = sW2
can vary from lab to lab.
is the average of the own variances of the different laboratories.