How Do I Create Histograms & Process Capability Reports in Excel
Histograms & Process Capability
Open the file Delivery Times.xls. This contains continuous data of hotel breakfast delivery times. Deviation Time is the deviation around targeted delivery time in minutes. The Critical Customer Requirements (CCR’s) are as follows: USL = 10 minutes late, LSL = -10 minutes (early).
Let’s begin with a view of the data using Histograms and Descriptive Statistics. Click
SigmaXL > Graphical Tools > Histograms & Descriptive Statistics.
Ensure that entire data table is selected. If not, check
Use Entire Data Table. Click Next.
Delivery Time Deviation, click Numeric Data Variable (Y) >>. Click
Note that the data has an average of 6, so on average the breakfast delivery is 6 minutes late. Also note the wide variation in delivery times (Stdev = 7.2 minutes). With the AD p-value > .05, this data can be assumed to have a normal distribution.
Click Sheet 1 Tab. Click
SigmaXL > Process Capability > Histograms & Process Capability
(or SigmaXL > Graphical Tools > Histograms & Process Capability).
Select Delivery Time Deviation,
click Numeric Data Variable (Y) >>. Enter
USL = 10, Target = 0,
LSL = -10, check Normal Curve as shown
Click OK. Resulting Histogram & Process Capability report is shown below:
With the Process Performance indices Pp and Ppk < 1, this process is clearly in need of improvement. Note that the difference between Pp and Ppk is due to the off-center process mean. (Cp and Cpk indices are provided in the Capability Combination Report or optionally when creating Control Charts).