The data you gather for the distribution analysis commands are individual failure times. For example, you might collect
failure times for units running at a given temperature. You might also collect samples of failure times under different
temperatures, or under different combinations of stress variables.
Life data are 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. This table 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 Distribution analysis (right censored
data).
• When your data have exact failures and a varied censoring scheme, including right-censoring, left-censoring, and
interval-censoring, see Distribution analysis (arbitrarily censored data).