Growth curves - interval data
main topic 

Use a paired response of start and end times when your data are interval failure/retirement times.

Enter your data in table form, using Start and End columns:

·    Start - the time at the start of the interval.

·    End - the time at the end of the interval.

·    System - identifies each system within a sample. You do not need a system column when you have only one system.

·    Frequency (or Cost) - the total cost of repairs or total frequency of failures at a particular time. See Using cost or frequency columns for more information.

This data set illustrates interval data, as well as the use of a frequency column.

Start

End

System

Frequency (or Cost)

0

1

1

2

1

5

1

4

9

*

1

0

0

4

2

2

5

7

2

4

10

*

2

0

8

9

3

4

5

8

3

2

11

*

3

0

In this example,

·    Two failures occurred between 0 and 1 hours for system 1

·    Observation ceased on system 1 at 9 hours

When you have more than one sample, you can use separate columns for each sample. Alternatively, you can stack all the samples in one column, then set up a column of grouping indicators. For an illustration, see Stacked vs. Unstacked data.

Each sample is analyzed independently and results in one growth curve. All the samples display on a single plot, with different colors and symbols to help you compare reliability growth between samples.

For general information on repairable systems data, see Data - Growth Curves.