The Telcordia Issue 4, Issue 3, and Issue 2 models calculate standard deviations for the failure rates for parts and assemblies. Under Prediction in the System file properties, Telcordia upper confidence level specifies the upper confidence level to use for these particular models. The default is 90. To have Telcordia Issue 3 or Issue 2 use some other confidence level, you enter the value. For more information, see Prediction System File Properties.

For each part, the standard deviation is calculated and stored in Failure Rate, Standard Deviation. This field and Failure Rate, Mean are used to calculate a predicted failure rate for the part. For each part, Failure Rate, Predicted displays the failure rate at the upper confidence level specified, taking into account the total quantity of this part in your system. When the default of 90% is used for the upper confidence level for Telcordia Issue 3 or Issue 2, you can compare the results in Failure Rate, Predicted to the results obtained from using Telcordia Issue 1.

The standard deviation for each child part is used to calculate the standard deviation for the assembly. This value is stored in Failure Rate, Standard Deviation. For an assembly, Failure Rate, Predicted is not the summation of the failure rates of its child parts. For each part, Failure Rate, Predicted is display-only. It is not directly used in the calculation of the Failure Rate, Predicted value for the assembly.

For an assembly, the value for Failure Rate, Predicted is calculated using the following three values: