Operator Bias Uncertainty Worksheet Features 
This drill-down worksheet provides a useful tool for evaluating measurement uncertainty due to operator bias or the error due to the perception or influence of a human operator.  While variations in human behavior and response lend this error source a somewhat random character, there may be tendencies and predilections inherent in a given operator that may persist from measurement to measurement.

The uncertainty due to operator bias is usually determined heuristically, linking it to parameter resolution or some other aspect of a measurement that can influence operator perception or behavior. With UncertaintyAnalyzer, it is estimated using the Operator Bias Uncertainty Worksheet, which is accessed by clicking the Operator Bias button on the Main Screen Error Source table.  The Worksheet contains separate tabs for estimating operator bias uncertainty for subject parameter readings and/or measuring parameter readings.

Subject (or Measuring) Parameter Specifications
This section of the Worksheet displays the subject (or measuring) parameter name, nominal or reading value, display resolution and display type. 
 
Subject (or Measuring) Parameter Operator Bias Uncertainty
This section of the Worksheet is used to estimate the subject (or measuring) parameter operator bias uncertainty from error limits and a containment probability (confidence level).  The error limits can be a combination of fixed ± limits, that can be estimated from experience, and ± limits based on percent or fraction (ppm) of the resolution of the parameter display or reading.  The probability that the operator bias is contained within the error limits is entered in the Conf. Level box. Alternatively, a coverage factor may be entered in the Cov. Factor box.
 
UncertaintyAnalyzer assumes that uncertainty due to operator bias is normally distributed unless the associated degrees of freedom are less than infinite or the % Confidence is 100%.   If the degrees of freedom are less than infinite and the % Confidence is less than 100%, the Student's t distribution is used to compute a standard uncertainty.  If the % Confidence is 100%, then the Uniform distribution is used and the degrees of freedom are assumed to be infinite.

 
In most cases, it would not be realistic to assume infinite knowledge about the operator bias uncertainty. The Type B Degrees of Freedom Calculator, which is accessed by clicking the button next to the Degrees of Freedom box, can be used to provide additional information about the uncertainty in the error limits and associated confidence level. In essence, it provides a means for incorporating a more realistic assessment of the "fuzziness" or lack of knowledge in our estimate. 

Operator Bias Uncertainty
The bottom section of the Worksheet displays the operator bias uncertainties for the subject parameter and the measuring parameter.   The appropriate Include box is checked to include subject parameter operator bias uncertainty or measuring parameter operator bias uncertainty in the total operator bias uncertainty. 

The correlation coefficient between these two sources of operator bias is also displayed (if applicable). If the operator biases for the subject parameter and measuring parameter are not correlated, then the Total Operator Bias Uncertainty is computed as the a root-sum-square (RSS) of the individual operator bias uncertainties. Otherwise, the value of the Total Operator Bias Uncertainty will reflect any correlation between the subject parameter and measuring parameter operator biases specified by you.

 
The Degrees of Freedom for the Total Operator Bias Uncertainty is computed using the Welch-Satterthwaite formula.