In measurement system analysis, how is bias defined?

In measurement system analysis, how is bias defined?

• A. The average difference between instrument readings and the true value across measurements.
• B. The maximum observed measurement error in a single reading.
• C. The standard deviation of repeated measurements.
• D. The difference between the most frequent and least frequent readings.

Answer: (A)

Bias is the systematic offset of a measurement process—the average difference between what the instrument reports and the true value across many measurements. It captures a consistent shift, not the random spread of results. For example, if you measure a standard value many times and the readings average 0.5 units higher than the true value, the bias is +0.5. This distinguishes bias from precision (how tightly results cluster, shown by the spread or standard deviation) and from extremes like the maximum error or range. In short, bias answers: on average, how far off is the measurement from the true value?

Bias is the systematic offset of a measurement process—the average difference between what the instrument reports and the true value across many measurements. It captures a consistent shift, not the random spread of results. For example, if you measure a standard value many times and the readings average 0.5 units higher than the true value, the bias is +0.5. This distinguishes bias from precision (how tightly results cluster, shown by the spread or standard deviation) and from extremes like the maximum error or range. In short, bias answers: on average, how far off is the measurement from the true value?