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by Dan Nelson

Correct Me If I’m Wrong
Don’t confuse the preventive aspects of corrective actions.





I once heard a gentleman offer a group of quality professionals the following explanation of corrective and preventive action: “If you sent your customers the wrong product, the corrective action would be to send them the right product. Then you would do a root cause analysis on that and take a preventive action to keep it from happening again.”

This example is misleading. It exemplifies a common misconception rather than dispelling it.

If you sent your customer the wrong product, you might correct the error by replacing it with the right product.

This action constitutes mere correction (i.e., eliminating a detected nonconformity). If, however, you act to eliminate the cause of the error, you’re taking a corrective action. Before any corrective action can be taken, one must first determine the cause of the error.

After determining a cause, any actions taken to eliminate that cause and its effects are corrective actions.

Effective corrective actions eliminate the cause’s underlying problems, thereby preventing such problems from recurring. Therefore, preventing a known problem from recurring is part of corrective action. In other words, a corrective action fixes the problem and all like it so it doesn’t happen again. There’s a preventive nature to corrective action.

Should the problem recur because of the same error, then the corrective action wasn’t effective for any of a variety of reasons (e.g., the root cause was misdiagnosed, the chosen action didn’t fully eliminate the cause or the action wasn’t properly implemented).

A preventive action, on the other hand, actually precludes potential problems from arising in the first place. Preventive actions operate only upon potential problems. They don’t prevent existing problems from recurring; corrective action does that.

For the hair-splitters, what follows is an example that contrasts corrective and preventive action by illustrating how a preventive action might arise in connec-tion with a corrective action.

In a manufacturing company, nonconforming product was found at a machining center. An investigating team determined that the parts were mistakenly loaded into the machine backward, which resulted in nonconforming product.

The team first reasoned that the problem might be caused because the parts were loaded into the machine by hand. However, further investigation into this hypothesis revealed that no problems had ever been detected with the other 20 part numbers that were also hand-loaded. The team decided that any action to control all hand-loaded parts merely because they were hand-loaded would add no value and prove counterproductive. The team concluded that the problem wasn’t specifically caused from hand-loading parts, but that these particular parts were prone to orientation errors.

Thus, the root cause was confirmed to involve “orientation errors.” To appropriately address the problem, any corrective actions would have to focus only on those parts that were prone to such errors.

The nonconforming parts were corrected (i.e., reworked). A jig was developed to prevent them from being loaded backward, thereby mistake-proofing this step in the process. This proved to be an effective corrective action because it eliminated the problem’s cause and was verified to prevent the problem from recurring.

Only one other part among the 20 was also subject to orientation errors, although as stated earlier, no problems had ever been detected with these parts. However, because the same root cause was recognized to exist in that circumstance, and with a similar probability of error, a jig was introduced for loading this part type as well. This action was still part of the original corrective action because the same cause--an orientation error--was being eliminated in another circumstance where it existed. Although this action might seem preventive because no problems had been encountered with this type of part, it was--strictly speaking--corrective because it eliminated another instance of the same existing cause.

Another of the 20 hand-loaded parts was very small and required particular attention to load into the machine. This part wasn’t subject to orientation errors, however, so the earlier corrective action, as defined, didn’t apply. Although no problems had ever been encountered with this part, the lessons learned from the previous corrective action suggested that a jig could mistake-proof the loading process for this part as well. Accordingly, a third jig was introduced to the process.

Introducing this jig into the loading process was a preventive action. Why? Because it prevented the occurrence of a potential problem whose cause was different from that addressed by the earlier corrective action. Because the third jig prevented potential problems from this new source, the similarity to the earlier problem doesn’t qualify this action as corrective. Rather, introducing the third jig was a bona fide preventive action.


About the author

Dan Nelson has worked with ISO 9000 for 10 years. Nelson is a QMS 2000 Principal Auditor (IRCA) and earned a master’s degree in business administration from the University of Iowa.

He consults under the business name Quality Crossroads.