t: Time Between Events

As an alternative to the g-Chart, we can instead monitor the amount of time between each event (rather than the number of non-events). This can be useful for data with no concept of a ‘non-event’ (i.e., there is nothing recorded until an actual event occurs).

The t Chart below monitors the number of days between each recorded surgical fatality.

To construct this chart, you provide the outcome variable of interest (number of days) in the ‘Outcome/Numerator’ field, and the date of each event in the ‘ID Key’ field, with one row per event (depicted below). The x-axis shows the event number rather than the date. Then, select t - Time Between Events from the Chart Type drop-down in Data Settings.