Conformity assessment: Acceptance control of test results – R

Repeatability and reproducibility conditions

[ISO 5725-6]

In many practical situations, there is seldom time or resources to repeat measurements more than just a few times. This section provides methods to check if a number (two, number, …) of measurement results, obtained under repeatability and reproducibility conditions,  are acceptable or if further testing is needed.

Only one measurement from each of two laboratories

The absolute difference between the two results is tested against the reproducibility limit, R.

  • If acceptable, then the two results are considered to be in agreement, and the arithmetic mean can be calculated as the end result.
  • If R is exceeded, then it is necessary to determine whether the difference in test results is due to poor precision of the method and / or a difference in the samples.

Multiple measurements from each of two laboratories

The absolute differences between the results is checked against the:

Critical difference, CD

as two arithmetic mean values of n1 and n2 measurements for the two laboratories:

Critical Difference

Critical Difference


ISO 5725-6: 1994 Use in practice of accuracy values


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