Statistics for Maintenance Modelling: Regression Modelling

# Assessing the Appropriateness of an Accelerated Life Model¤

So far we have discussed the concept of the accelerated life model, but how do we know if the accelerated life model is appropriate for our data set? As an initial guide the following plot can be used:

If the data are grouped, the jth group of nj observed failure times having x = j and nj being large enough for a plot of the sample survival j(t) function against ln t, then the plot should resemble horizontally shifted copies of the baseline plot of S0(t) against ln t. This follows from:

Sj(t) = S0(tj) = S0{} = s0(y + ln j),

with y = ln t say. S0 represents the survival function of the log failure time when j = 1.

See the case study later in this session for an example of using this plot (screen 11).

The above plot applies to censored data as well as uncensored data, in which case, the Kaplan-Meier estimator (see the Nonparametric Estimates of the Survival Function screen in the Model Selection session) is used for .

This plot, and variations of them, are also used when assessing the appropriateness of proportional odds models and proportional hazards models, which are discussed in the next few screens.

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