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T-Chart (Rare Event Control Chart)¶
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QXL Stat Tools Tab > Control Charts > T-Chart
The T-Chart is a rare event chart which should be used when the count between times is less than 1.(Wheeler, D. J. "Working with Rare Events." Quality Digest. Quality Digest, Web. 10/28/11.)
For example, the following dataset reflects the times between fires in a local area. The first data point, 122, indicates that 122 days passed between fires. In this dataset, the count between times is far less than 1.
The T-Chart is applied to the measured time between events. The data can be in the measured time between events as above, or you can enter the date and time the event occurred. For example, the above data can be also be expressed with this dataset.
Note that the first date (1 Jan 2000 at 1:02) establishes the first event. The second time (2 May 2000 9:15) occurred 122.343 days later.
The T-Chart should not be confused with the G-Chart. The G-Chart is used when the time between events is a count. The T-Chart is used when the time between events is a measurement (continuous).