Corrective Action and Preventive Action:
There is a difference

This seems to be an area where there is a lot of confusion. While most understand that corrective action is taken to eliminate the cause of a detected nonconformity, there is not as clear an understanding of preventive action. One reason for this is that corrective action is also taken to prevent recurrence once the cause is determined.

Preventive action is taken to eliminate the cause of a potential nonconformity. Potential being the key word. In other words, you're preventing the problem before it occurs. If the problem has not occurred, how do you know it's a problem? This is one of the reasons for the requirement in ISO 9001:2000 for analysis of data (clause 8.4) […to provide information regarding trends of processes and products to identify opportunities for preventive action.] A worsening trend may indicate a need for preventive action. Of course, it can also be an idea generated by observation of daily work activities.

Along these same lines, correction is not the same thing as corrective action. Correction is elimination of the nonconformity, while corrective action is elimination of the cause of the of a nonconformity. A correction can be made in conjunction with a corrective action. It can also be rework on nonconforming product to make it conform to requirements (see our article on Nonconformity vs. Nonconformance).

When do you take corrective or preventive action?

Here is an example:

A process produces widgets. The widgets are measured at the end of the process to determine conformance to requirements. Reasons for any nonconformity are tracked on a regular basis.

Consider the following scenarios:

Individual widgets that do not meet requirements are considered nonconforming product and handled accordingly. The nonconformities are corrected, but corrective action requests are not issued. Why not? The supervisor notices a worsening trend in one of the product characteristics, although the widgets are still considered conforming. A preventive action request is issued. The supervisor notices an increase in a particular type of nonconformity. A corrective action request is issued. In the first situation, corrective action requests are not issued because a single nonconformity does not provide enough information for investigation. In the second case, the cause can be eliminated before a large amount of nonconforming product is corrected.

Note: Processes are different and will have different thresholds for preventive and corrective action.