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Stat > Reliability/Survival > Repairable System Analysis > Nonparametric Growth Curve

Select the option that best describes your data.

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Data are exact failure/retirement times

Complete the following steps if your data indicate the exact time that each item failed or was retired from service.

  1. In Variables/Start variables, enter the column or columns that contain the exact failure or retirement times. Enter one column per sample. Minitab assumes that all the data within each column are from identical processes.
  2. If the failure data in a column is from multiple systems, under System Information, select System ID. Then enter one column of system IDs for each sample. If a single response column represents more than one system, you must use a system ID column.
    Note

    You cannot specify the number of systems if you have exact data. The number of systems can only be specified with interval data.

  3. If all the samples are stacked in one column, but belong to separate groups, select By variable and enter a column of grouping indicators. Minitab provides a separate growth curve analysis for each group.
In the following worksheet, the Time column contains exact failure/retirement times. The System column (optional) identifies the system for each failure time. Because the data are both time-truncated and failure-truncated, the Retirement column indicates whether the data in each row is a failure time or a retirement time. By default, the lower value in the column (0) indicates a retirement time and the higher value (1) indicates a failure time. For example, system 1 failed at 1 hour, failed at 5 hours, and was retired at 9 hours.
C1 C2 C3
Time System Retirement
1 1 1
5 1 1
9 1 0
4 2 1
7 2 1
10 2 0
8 3 1
9 3 1
11 3 0

Data are interval failure/retirement times

Complete the following steps if your data indicate only that the item failed or was retired from service between two specific times.

  1. In Variables/Start variables, enter the column or columns that contain the start times. Enter one column per sample. Minitab assumes that all the data within each column are from identical processes.
  2. In End variables, enter the column or columns that contain the end times. Enter one column per sample. Use a missing value symbol for an end time to indicate that the start time was the retirement time for a system.
  3. If the failure data in a column is from multiple systems, under System Information, select an option to indicate how to enter the system information.
    • System ID: Select this option to identify the systems within the sample, then enter one column of system IDs for each sample. If a single response column represents more than one system, you must use a System ID column.
    • Number of systems: Select this option if you have data for multiple systems but are not entering system IDs. Enter a column to specify the total number of systems (number of trials) in each interval.
      Note

      If you select this option, you must also enter a Cost/Frequency column to indicate the total number or failures (number of events) or the total cost of failures for the systems within each interval. For more information, go to Specify repair cost or frequency for Nonparametric Growth Curve.

  4. If all the samples are stacked in one column, but belong to separate groups, select By variable and enter a column of grouping indicators. Minitab provides a separate growth curve analysis for each group.
In the following worksheet, the Start column and End column indicate the interval within which each failure (or retirement) occurred. The System column identifies the system for each failure time. For example, a failure occurred between 0 and 1 hour for system 1. Another failure occurred between 1 and 5 hours for system 1. After 9 hours, no more observations were recorded for system 1.
C1 C2 C3
Start End System
0 1 1
1 5 1
9 * 1
0 4 2
5 7 2
10 * 2
8 9 3
9 8 3
11 * 3
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