SBC - A Shift in Thinking

Derek BDerek B PQ Systems Employee
You perform a capability study and learn that your Cpk is 1.5.  Party time, right?

Not necessarily...

Stability must be assessed before a capability study is done.  Without this prerequisite, the Cpk statistics are not reliable.

In other words...  If you don't yet have a process which is statistically in control (verified by control charts and testing), you don't yet have a predictable process.  If you don't have a predictable process, then how appropriate is it to comment on the capability of meeting some target in the future?

If you've fallen into this trap before, you're definitely not alone.  We've all heard of "SPC" before.  I'd like to challenge you to change your thinking; start practicing SBC - Stability Before Capability.  The result will be better processes, better (and meaningful) results and happier customers.

What do you think?
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