I am struggling with the definition of Cost of Quality.
Glossary defines COQ as"
"Cost of quality (COQ): Another term for COPQ. It is considered by some to be synonymous with COPQ but is considered by others to be unique. While the two concepts emphasize the same ideas, some disagree as to which concept came first and which categories are included in each".
My proposal: To avoid confusion that Appraisal and Prevention are not due to Poor Quality, All 4 cost categories are typically grouped under COQ. The internal and external failure costs are grouped specifically under COPQ. i.e COPQ is a subset of COQ. We could also separate Appraisal and Prevention costs to COGQ Cost of Good Quality. (Also refer to the book Principles of Quality Cost).