My last post, "Defining Quality," generated a number of thoughtful comments from readers. I really appreciate hearing other perspectives on the questions I posed in the post, especially this comment:

Only in the world of utopia are there processes with zero variation and where only Green or on target values are produced. In the real world you have to look at each process and determine the ability and cost required to reduce process variability. In some cases it may be more cost effective to use an inspection system (like a vision system) to inspect out defects, then it would be to reduce the variation that creates these defects. The rule I use is if prevention is not practical and if detection methods are effective and reliable, then the inspection method is the right choice. When detection is difficult or not reliable, then prevention efforts must be taken.

This got me thinking about a model for inspection that I’ve found helpful in recent years.

If you look at this carefully, you’ll see that it is a typical "Input - Process - Output" diagram. If you look at it even more carefully you’ll see that it is there are two loops on the graphic. The question isn’t so much which loop is right and which is wrong. The question is: Which loop is primary? Which loop is emphasized?

Both loops start in the middle with an observation or a measurement. The right-hand loop is the Voice of the Customer. I’ve highlighted it here in yellow:

The right-hand loop compares the observation to the customer’s requirements and asks "Does this meet the customer’s requirements?" If it passes, you can ship the product. If it doesn’t, you have a couple of options.

If your product fails to meet specs in a manufacturing environment, your options are to scrap, rework or downgrade the product. In a transactional world, your options are to remediate, replace or compensate. In either situation your options for response are always reactive and wasteful.

I see people tolerate this waste for all kinds of reasons. Perhaps there are other, more expensive issues that need to be addressed before this problem can be tackled. Perhaps the cost of getting rid of a problem seems too high. Perhaps they’re just used to it and can’t imagine any other way of doing business. Some of these reasons are probably better than others, and I’m really not here to pass judgment in this blog. The point that I want to be clear about is that the right hand loop - the Voice of the Customer Loop - captures waste and protects the customer. There is nothing wrong with that - actually there are some good things about it. But it doesn’t prevent the problems from recurring. The left hand loop starts at the same place, but has a very different impact. This is the Voice of the Process Loop, highlighted here in green:

The Voice of the Process Loop also requires an observation or a measurement, but here is the crucial difference. Where the Voice of Customer Loop compared the observation against specifications, the Voice of the Process Loop compares the observation against what is expected.

On what do we base our expectations? Well, you can guess that it isn’t a specification - or anything that is derived from a specification or a requirement.

We base our expectations on our past experience with the process. This is why we call it the Voice of the Process. The best way to tap into our past experience with the process is with the humble control chart. The control chart tells us what we need to know about the process. If the data we observe shows no patterns, no shifts in mean, and no more variation than we’ve experienced before, then we have reason to conclude that the process is stable. Once we know the process is stable, then we can still ask ourselves is there a way to improve (reduce) chronic variation? This can lead to improvements in the process or the inputs to the process.

If the process tells us that it isn’t stable, then we can (and should) address that. We can focus our efforts on improving the process or the inputs to the process.

Using the left-hand loop - the Voice of the Process Loop - is how you improve processes and ultimately reduce or even eliminate the need for the Voice of Customer Loop. In an ideal world our processes are well understood and stable, and we don’t need to check against specs because we know that we’ll always meet customer requirements.

In the meantime, we live in the real world. In the real world, inspections against specifications are a reality and will probably be around for a long time. They’re useful and I would be the last to advocate their complete elimination.

But they don’t lead to process or quality improvement, or to an elimination of the waste associated with failure to meet requirements. To get there you need to pay attention to the Voice of the Process. You need to stabilize your processes and then systematically reduce chronic variation.

Where is your emphasis? Which loop do you follow? What are the biggest challenges you face or have faced in shifting your emphasis to the Voice of the Process Loop?