What is a Cox-Snell residual?

Cox-Snell residuals are a type of standardized residuals used in reliability analysis. A residual is the difference between an observed data point and a predicted or fitted value. A Cox-Snell residual considers the distribution and estimated parameters from the lifetime regression model.

The Cox-Snell residuals are equal to the negative of the natural log of the survival probability for each observation.

Minitab displays the Cox-Snell residuals for regression with life data and accelerated life test models on an exponential probability plot so that you can do the following tasks:
  • Identify extreme observations that need additional investigation.
  • Assess whether the failure time or log failure time distribution is appropriate.
  • Assess whether the relationship between the failure time or log failure time and the stress variables in an accelerated life test is appropriate.

This graph indicates an extreme observation.

This graph indicates that either the failure time distribution or the relationship between failure time and stress is not appropriate.

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