2. Measurement Process Characterization
2.3. Calibration
2.3.3. What are calibration designs?

2.3.3.1.

Elimination of special types of bias

Assumptions which may be violated

Two of the usual assumptions relating to calibration measurements are not always valid and result in biases. These assumptions are:

• Bias is canceled by taking the difference between the measurement on the test item and the measurement on the reference standard
• Reference standards and test items remain stable throughout the measurement sequence

Ideal situation

In the ideal situation, bias is eliminated by taking the difference between a measurement X on the test item and a measurement R on the reference standard. However, there are situations where the ideal is not satisfied:

• Left-right (or constant instrument) bias
• Bias caused by instrument drift