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

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:

mis the accepted reference (or “true”) value

bis the bias

eis the random error in each measurement

### Bias

#### The bias, *b***, of a laboratory**

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) =s_{L}^{2}

The variance in the error for each laboratory:

Var(e) =s_{W}^{2}

can vary from lab to lab.

#### Repeatability variance

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

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