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Nevada Chart Format

Statistical Process Control

The Nevada chart format includes a statistical process control (SPC) method for analyzing warranty returns data. The SPC method evaluates the discrepancy between the actual number of failures and the number of failures predicted by the distribution parameters. It uses a chi-squared test to help you detect unusually high or low return rates for any given period, alerting you to any possible deviations in manufacturing, quality control or any other factors that may adversely affect the reliability of the product in the field. This enables you to intervene immediately and avoid increased warranty costs or more serious repercussions. The SPC application is available only for the Nevada chart format.

Note: The SPC feature applies only to homogeneous data sets and is therefore unavailable when you select the Use Subsets option on the Main page of the control panel.

To use SPC, click the Statistical Process Control page icon on the control panel.

Tip: If you wish to perform a manual evaluation of the table of chi-squared values, you can use Weibull++’s Quick Statistical Reference (QSR) tool to look up chi-squared values for different control values and degrees of freedom. You can access the QSR by choosing Home > Synthesis > Quick Tools > Quick Statistical Reference.

 

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