Computing CPK for bimodal data, either large readings or zero (majority)..

Question

Hi,

I have data points from measurements of a certain defect. The readings are either zero(majority) or high readings.

For example: How do i get the CPK if the USL is 100? Desirable is the zero reading.

60.176.87668.343.960.342.866.149.462.149.866.561.258.859.160.367.268.554.661.064.257.700000000000000000000000000000000000000

Steven_Moore · Answer

jabenir,  There is one fundamental question you have to answer before calculating Capability Indices:  Is your process in statistical control?  If the process is not in a "reasonable degree of control", then Capability Analysis is meaningless.  As Dr. Wheeler says in one of his books:  "What can be said for the capability of a process not I statistical control?  Not much!"

Other questions that need to be answered BEFORE a Capability Analysis:  Is the data you presented in time order?  If not, what is the order and what does a Runs Chart and/or Process Behavior Chart look like?  Can you determine defect rates for discrete periods of time with rational sub-grouping?

txnelson · Answer

I suggest that you use the Distribution Platform, to help you determine the best way to calculate the Cp/Cpk.  If you startup the Distribution Platform, and then under the red triangle, go to:

Continuous Fit==>All

it will help you determine which distribution best fits your data, and then under that distribution, it will give you the Cp/Cpk.