Failure times
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The response data you gather for the regression with life data commands are the individual failure times. For example, you might collect failure times for units running at a given temperature. You might also collect samples under different temperatures, or under varying conditions of any combination of accelerating variables.

Individual failure times are the same type of data used for Distribution Analysis.

Life data is often censored or incomplete in some way. Suppose you are monitoring air conditioner fans to find out the percentage of fans that fail within a three-year warranty period. The table below describes the types of observations you can have:

Type of observation

Description

Example

Exact failure time

You know exactly when the failure occurred.

The fan failed at exactly 500 days.

Right censored

You only know that the failure occurred after a particular time.

The fan had not yet failed at 500 days.

Left censored

You only know that the failure occurred before a particular time.

The fan failed sometime before 500 days.

Interval censored

You only know that the failure occurred between two particular times.

The fan failed sometime between 475 and 500 days.

How you set up your worksheet depends, in part, on the type of censoring you have:

·    When your data consist of exact failures and right-censored observations, see Uncensored/right censored data.

·    When your data have a varied censoring scheme, see Uncensored/arbitrarily censored data.