Example of X and S chart
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You are conducting a study on the blood glucose levels of 9 patients who are on strict diets and exercise routines. To monitor the mean and standard deviation of the blood glucose levels of your patients, create an X and S chart. You take a blood glucose reading every day for each patient for 20 days.

1    Open the worksheet BLOODSUGAR.MTW.

2    Choose Stat > Control Charts > Variables Charts for Subgroups > Xbar-S.

3    Choose All observations for a chart are in one column, then enter Glucoselevel.

4    In Subgroup sizes, enter 9. Click OK.

Graph window output

Interpreting the results

The glucose level means and standard deviations over the 10-day period fall within the control limits. The glucose level and its variability are in control for the nine patients on the diet and exercise program.