Control Chart Examples in Excel

A control chart monitors process performance and identifies process shifts. Control charts can be used in many ways to monitor:

• Any product specification over time
• Number or percent of defects
• Financial performance

Control Chart Example - Product Specifications

The most common type of control chart used to monitor a product specification is an "X" chart: XmR, XbarR or XbarS chart.

XmR Chart - Individuals and Moving Range

In this control chart example. we're measuring an individual piston ring diameter using an XmR chart. The XmR or Individuals and Moving Range chart has two charts: one shows individual measurements over time and the other monitors the range (i.e., difference) between measurements.

In this control chart example, while the X chart appears to be in control, the range chart shows a potentially unstable condition: too many points in a row hugging the center line. The QI Macros SPC Software for Excel highlights all potentially unstable (i.e., out of control) points in read.

Most manufacturing applications measure five or more samples at a time to form a single subgroup. The five are then averaged to create a XbarR charts or XbarS charts.

X bar R - Average and Range Chart

Using five samples per subgroup in this control chart example, the variation in range shows that it's in control.

With five samples per subgroup, you could also use the X bar S Chart - Average and Standard Deviation.

X bar S - Average and Standard Deviation Chart

Control Chart Example - Defects

Another common type of control chart involves measuring defects and defect rates.

P Chart - Fraction Defective

U Chart - Number Defective

C Chart - Number Defective

NP Chart - Number Defective

XmR Individual Moving Range Chart - Defect Rate

In the control chart example below, the XmR chart shows patient falls per 1000 patient days. The downward trend (red below) was caused by an improvement project. The limits were changed to reflect the new process performance: less variation and lower falls rate.

Control Chart Example - Financials

Another use of control charts involves financials like revenue, expenses and costs. Because Six Sigma focuses on reducing costs to boost profits, the XmR chart can be useful to detect performance.

The control chart example below shows denied insurance claims. It shows that the process is in control and costs over a million a month in denied claims.

• Watch video creating a control chart in Excel using the QI Macros
• Use of a control chart - how do I interpret the results?
• Types of control charts
• How do I choose the right chart?
  With a control chart decision tree!
• Control chart in Excel

Control charts are just one of the tools included in the QI Macros for Excel SPC Software for Excel.

Download the FREE 30-day Evaluation copy of the QI Macros Excel SPC Software for Six Sigma