## Practical implementation of the definitions of trueness and precision in accuracy experiments

ISO 5725-1 (1994)

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

## Statistical model of accuracy experiment

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

### Bias

is estimated as

while

#### The bias, B, in the measurement method

where u ref the accepted reference (or “true”) value.

### Variance

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.

#### Repeatability variance

is the average of the own variances of the different laboratories.