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2. Measurement Process Characterization
2.4. Gauge R & R studies
2.4.5. Analysis of bias

Remedial actions and strategies

Variability The variability of the gauge in its normal operating mode needs to be examined in light of measurement requirements.

If the standard deviation is too large, relative to requirements, the uncertainty can be reduced by making repeated measurements and taking advantage of the standard deviation of the average (which is reduced by a factor of \( 1/\!\sqrt{n} \) when \( n \) measurements are averaged).

Causes of excess variability If multiple measurements are not economically feasible in the workload, then the performance of the gauge must be improved. Causes of variability which should be examined are:
  • Wear
  • Environmental effects such as humidity
  • Temperature excursions
  • Operator technique
Resolution There is no remedy for a gauge with insufficient resolution. The gauge will need to be replaced with a better gauge.
Lack of linearity Lack of linearity can be dealt with by correcting the output of the gauge to account for bias that is dependent on the level of the stimulus. Lack of linearity can be tolerated (left uncorrected) if it does not increase the uncertainty of the measurement result beyond its requirement.
Drift It would be very difficult to correct a gauge for drift unless there is sufficient history to document the direction and size of the drift. Drift can be tolerated if it does not increase the uncertainty of the measurement result beyond its requirement.
Differences among gauges or configurations Significant differences among gauges/configurations can be treated in one of two ways:
  1. By correcting each measurement for the bias of the specific gauge/configuration.
  2. By accepting the difference as part of the uncertainty of the measurement process.
Differences among operators Differences among operators can be viewed in the same way as differences among gauges. However, an operator who is incapable of making measurements to the required precision because of an untreatable condition, such as a vision problem, should be re-assigned to other tasks.
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