How Do I Create P-Charts in Excel Using SigmaXL?

P-Charts

1. Open New York Daily Cycle Time – Discrete.xlsx. This is data from the Sigma Savings and Loans Company, New York location. Each day, the cycle time (in days) for completed loans and leases was recorded. N indicates the number of loans counted. A Fail was recorded if the cycle time exceeded the critical customer requirement of 8 days. Note that we are not recommending that continuous data be converted to discrete data in this manner, but rather using this data to illustrate the use of P charts for Discrete or Attribute data. P Charts (for Defectives) can have fixed or varying subgroup sizes.


2. Select SigmaXL > Control Charts > Attribute Charts> P. Ensure that B3:E23 are selected, click Next.


3. Select Fail, click Numeric Data Variable (Y) >>; select N, click Subgroup Column or Size >>. If we had a fixed subgroup size, the numerical value of the subgroup size could be entered instead of Column N. Check Tests for Special Causes.

   
   

   
   
4. Click OK. The resulting P-Chart is shown:



The moving limits are due to the varying sample sizes. While this P-chart shows stability, a much bigger concern is the average 41% failure rate to deliver the loans/leases in 8 days or less!

P-Charts: Advanced Limit Options – Historical Groups

1. Open New York Daily Cycle Time Discrete – Before After Improvement.xlsx. Before_After denotes before improvement and after improvement. We would like to use a P-Chart with historical groups to split the limits demonstrating the before versus after improvement.


2. Click SigmaXL > Control Charts > Attribute Charts > P. Ensure that the entire data table is selected. If not, check Use Entire Data Table. Click Next.


3. Select Fail, click Numeric Data Variable (Y) >>; select N, click Subgroup Column or Size >>.


4. Click Advanced Options. Select Specify Historical Group Column. Select Before_After, click Historical Groups >>.




5. Click OK. The resulting P-Chart with split limits based on historical groups is shown, demonstrating a clear process improvement: