Overview of Distribution ID Plot

Use Distribution ID Plot to determine which distribution best fits your data. This analysis allows you to evaluate the fit of 11 parametric distributions that are commonly used to model reliability data: smallest extreme value, Weibull, 3-parameter Weibull, exponential, 2-parameter exponential, normal, lognormal, 3-parameter lognormal, logistic, loglogistic, and 3-parameter loglogistic.

Minitab creates probability plots for the distributions that you select. The probability plots help you determine which, if any, of the parametric distributions best fits your data. In addition, Minitab calculates percentiles and mean time to failure (MTTF) values for each distribution, which provide additional information to consider when selecting a distribution model for reliability analysis. Distribution ID Plot can also help you determine whether to use a parametric or nonparametric distribution analysis to further evaluate your data.

Use this analysis for exact failure times or for any censoring scheme.

Exact failure data: Record the failure time at a fixed point in time before the end of the study or reliability test
Right-censored data: Record a time when the unit still survived at the end of the study or reliability test. For example, a patient may quit a study before it ends, or a unit is still operating after the allocated testing time. The exact failure time is unknown but will certainly occur beyond the allocated study time.
Interval-censored data: The exact failure time is unknown, but it occurred in a known interval. For example, a unit was still operating at 12 when the reliability engineer left for a mid-day break. Upon the engineer’s return at 12:30 they noticed that the unit has failed. Thus, the unit failed in the interval starting at 12 and ending at 12:30.
Left-censored data: Left-censored data is a special case of interval-censored data point where the beginning point of the interval may be time 0 or may be unknown. The engineer only knows that the unit failed by some specific time since the beginning of the reliability test.

In this analysis, interval censoring allows for the specification of left-censored data and data that combine different types of censoring. For more information, go to Data censoring.

Tip

The analysis stores a reliability data definition that includes the sample columns and the censoring scheme. Select the definition to quickly run Distribution ID Plot, Distribution Overview Plot, Parametric Distribution Analysis, and Nonparametric Distribution Analysis on the same data.

Where to find this analysis

To create a distribution ID plot, choose Stat > Reliability/Survival > Distribution Analysis > Distribution ID Plot.