Data considerations for G Chart

To ensure that your results are valid, consider the following guidelines when you collect data, perform the analysis, and interpret your results.

The data should be either the number of opportunities between rare events or the number of days between rare events

If your data are the exact time and date of each event or elapsed time between events, use T Chart.

When the data are the number of days between events, the number of patients or procedures per day must be relatively constant

If the number of opportunities per day is not relatively constant, the chart may provide misleading results.

The data should follow a geometric distribution

If the data do not follow a geometric distribution, use an attribute chart, such as P Chart or U Chart.

The data should be in time order

Because control charts detect changes over time, the order of the data is important. You should enter the data in the order it was collected, with the oldest data at the top of the worksheet.