Identifying stratification

When data are collected under a variety of different conditions the meaning of the data can be hard to see. Stratification within a process can lead to hidden underlying patterns.

  1. On the Analyse-it ribbon tab, in the Process Control group, click Stratification.
    In the analysis task pane, the Control Chart panel is displayed.
  2. In the Color / Symbol drop-down list, select Operator.
  3. Click Recalculate.

Control chart points are plotted using a symbol and color depending on the operator. It is easy to see that the operator SNH was responsible when the out-of-control signals occurred.

Stratified Xbar-R control chart(click to enlarge)

After investigating the causes of the out-of-control condition we document them in the worksheet alongside the data.