Corrective Action... and "Whac-A-Mole"

While “Corrective Action” is an essential component for any quality management system, surprisingly few quality professionals have a good understanding of it. This is most often because so many quality professionals lack a basic understanding of “Common Cause” vs “Special Cause” variation in a process.

Imagine that you frequent a particular restaurant. The service and food are typically great, but occasionally you find that the silverware (rolled in a napkin) is missing a piece… or has two of the same piece while missing the third piece (e.g., two forks and no knife). Whenever this happens, you simply inform the server, who immediately provides you another napkin neatly rolled around all of the required silverware. The “nonconforming” condition is quickly and easily corrected.

The staff is well trained, and rarely make these mistakes. If one were to initiate a “corrective action” to address this situation, it would quickly prove futile because there is NO “assignable” root cause to be eliminated. This type of error is a normal, random (common cause) variation in the restaurant's process due to the volume of silverware that is washed, sorted, and manually rolled into napkins by the staff.

However, one night you arrive and order dinner only to find that the food takes much longer than normal to arrive at your table, has been over-cooked, and is cold. You complain to the server who apologizes explaining that their chef is unexpectedly absent tonight due to an illness. And that this was terrible timing because his Assistant chef is traveling on vacation. Consequently, a replacement chef, who is unfamiliar with both their kitchen and menu, had to be brought in to fill this temporary need.

Unlike the silverware issue, this is an unusual / abnormal, situation that has not previously occurred. Therefore, this would be a “special cause” variation in their process with an assignable root cause). Special causes produce systematic effects/errors in a process.

However, had there been an unusual condition leading to excessive debris on the bike train (e.g., such as high winds or a tornado through the area), then this would have been a “Special Cause” variation (i.e., an “unnatural pattern” in the process, which is unusual, not previously observed, non-quantifiable variation in the process with an assignable root cause). Special causes produce systematic effects/errors in a process.

Because far too many quality professionals fail to differentiate between “Common Cause” and “Special Cause” variations in a process, a very large number of nonconformities from “Common Cause” variations are incorrectly addressed through the corrective action process. This leads to a cycle resembling the 1976 arcade game, “Whac-A-Mole” (where moles pop up from their holes at random, and the player earns points by forcing them back into their hole through hitting them directly on the head with a mallet). In the end, nothing is accomplished… but the player has a false sense of accomplishment reflected by their score. In this case, the quality team “feels” good (a false sense of accomplishment) about the apparent (short term) success of each corrective action.

Only through first determining whether each nonconformity is a “Common Cause” or “Special Cause” variation, can “real” corrective action can be realized.

In order to properly implement a “corrective action”, there must be an assignable “root cause”. And in order for there to be an assignable “root cause”, the nonconforming condition must be the result of a “special cause” variation (i.e., an “unnatural pattern” in the process, which is unusual, not previously observed, non-quantifiable variation in the process).

Consequently, because “special causes” produce systematic effects/errors in a process, properly implemented “corrective actions” are reactive process improvements… refining an existing process.

Because “common cause” variations are inherent to the existing process, these variations can only be eliminated by significantly “modifying” or “re-designing” the existing process. The most effective process improvement activities are realized through applying the Lean Six Sigma concepts & methodologies.

As a process is being “modified” or “re-designed”, one of the best tools to use is the "Failure Mode and Effects Analysis" (FMEA)… or FMECA (“Failure Mode, Effects and Criticality Analysis”).