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David Kerridge

Quality Insider

Improving a Process

The late David Kerridge on taking a system approach

Published: Thursday, June 13, 2013 - 16:12

Editor’s note: Distinguished statistician and essayist David Kerridge passed away last month in Aberdeen, Scotland, at the age of 81. The former head of statistics at Aberdeen University, Kerridge was a leader in the British Deming Association and lectured with W. Edwards Deming.

There is not one way to improve a process, but many. These are not alternatives. Used with understanding, all contribute to the continual improvement of every process and the whole system. Each makes other methods more effective, and so they should be used together. To illustrate this, we concentrate on the practical problems of using the Deming cycle, and show how other actions help it work.

Note: Deming called the cycle the “Shewhart cycle.” Others call it the “PDSA cycle (for plan-do-study-act),” and the Japanese call it the “Deming wheel.” It was certainly given its present form by W. Edwards Deming, so it seems fair to name it after him.

A unified approach

This combined and unified approach to improvement is typical of the Deming philosophy. Instead of learning one technique and applying it as much as we can, we take a system view. This fits in with the way we tackle anything complicated. An automobile is simple compared to most processes. If we want it to run well, we don’t spend all our time on the electrical system and ignore the fuel supply, or concentrate on the tires and forget the brakes. If there is a breakdown, it probably affects just one part of the car, and naturally we find out which, and work on that first. But for trouble-free motoring, we make sure that all the essential parts are regularly serviced. We don’t wait for something to go wrong.

Seven ways to improve a process

These improvements are expressed as a list of actions and questions. Anyone may produce dramatic improvement on its own. For example, improvement in the measurement process, even though it does not directly affect the process, may reduce tampering. More often it is the interaction between these approaches that produces results. What’s more, we must see the investigation of this one process as part of the transformation of the whole organization.

Without overall change, it’s hard to improve an individual process, and the improvement, even if we achieve it, seldom lasts. But equally, working on a process can make some of the ideas behind overall transformation more concrete, and fix them in people’s minds.

The seven ways to improve a process are:
1. Study the customers’ needs. Is the output of our process the most helpful that could be given to them? Is it causing problems in a later process? There’s no point in improving a process until you know what a good result really means.
2. Flowchart the process. Are there unnecessary stages, or examples of rules 2 to 4 of Deming’s funnel experiment? Have you identified all the internal and external customers and suppliers? Do you listen to them?
3. Improve the training of the process operators. Introduce operational definitions.
4. Study ways to measure outputs and inputs. What measures are most relevant to the success of the process? Check that the measurement processes are under statistical control before attempting to use the measurements to study the process.
5. Reduce variability of the inputs. The inputs include every way in which the rest of the system affects the process. Can you reduce the numbers of internal or external suppliers to the process? Do the suppliers understand your process?
6. Plot the outputs and inputs on statistical process control (SPC) charts. Remove special causes. Eliminate tampering.
7. Collect suggestions for improving the process, and test them using the Deming cycle.

There are more ways to improve a process, but these are enough to make the point. The Deming cycle relies on checking the results of a change, using measurement. When the process itself varies less, and measurements on it are more accurate, it is easy to see the effect of a change. Besides which, the understanding of the process that comes from all these different ways of studying it will suggest changes that should be tried.

What should we do first?

For an individual process that has not been studied before, the order given above is reasonably good. This does not mean that we finish one before going on to the next: We usually do several at the same time.

Even if the process suffers from a major problem that must be solved, don’t neglect the general, systematic, approach. There’s a good reason for this. If the cause of the problem had been obvious, such as something broken, it would have been put right immediately. So we expect the investigation to take time. Occasionally a problem disappears, still unexplained, as a part of overall improvement. Most often the cause is easier to trace when systematic improvement is underway.

It is so natural to rely on troubleshooting that some examples of it are in order. One process had consistently bad results over many years. Every so often a troubleshooting team went out from the head office, found a problem, and fixed it. But soon things were just as bad as before. Then control charts were plotted for inputs and outputs, and the process improved without further specific action. In another case, a long-standing problem disappeared after a change to a single supplier.

Applying the Deming cycle

Because it relies on stability, as well as on good measurements, the Deming cycle is most effective when the other six approaches to systematic improvement are underway. It is not a recipe, but a system: In other words, it does not tell us what to do, but how to make what we choose to do systematic and effective.

We must first decide on which change we should try. This is part of the “plan” stage of plan-do-study-act (PDSA). There will usually be plenty of ideas to choose from, provided everyone understands that learning about the process is more important than guessing the “right” answer. So no one is blamed for making the wrong guess. After all, even if a change does make things worse, it will suggest ways to make things better.

We can only test one change at once, so if there are many suggestions, we need ways to choose between them. Here are some key questions:
1. Can it be tested on a small scale?
2. Will the effect be seen reasonably quickly?
3. Will the effect be easy to measure?
4. Does the test require new measurements, or will existing measurements be sufficient?
5. Has the measurement already been studied and shown to be stable?
6. Is the test simple to do?
7. Will it take long to do?
8. Can the test be done without disturbing the ordinary running of the process?

Obviously if the answer is “yes” to all these questions, the change should be tried as soon as possible. We will seldom be so fortunate, but the number of yes answers gives a crude order of priority among different possible changes. Often practical considerations, like the need to maintain the enthusiasm of the team, will provide the deciding vote.

There is, however, one general principle that might be overlooked. In the long run, a change that reduces variation, without making the average worse, is more desirable than one that improves the average, leaving the variation as great as before. This is because reduced variation makes other improvements easier to find.

Be systematic

Once a choice has been made, make sure that you do not waste any of the information from the experiment. Keep systematic records of each stage. Don’t rely on memory; it plays too many tricks.

Using the Deming cycle doesn’t just help to improve the process. It also has great educational value for everyone who takes part in it. It develops teamwork. Ideas at the “plan” stage will often be wrong, and many cherished ideas disproved. Members of the team will learn not to trust guesswork, but to use theory, and yet rely on facts. They will also see the practical value of theory, measurement, and operational definitions. These things will affect their whole attitude to transformation.

Synthesizing the Uncommon Common Sense

David Kerridge was one of the leading Deming proponents in the world, yet how many people have heard of him? This dry, somewhat reticent Scottish academic became part of a panel that aided Deming in his seminars the last few years of his life, which is how I first encountered him. He was very quiet and direct in his presentations and had a brilliant gift for synthesizing the “uncommon common sense” of Deming’s philosophy, as I discovered in his subsequent writings.

Note that he was a former academic head of statistics—and I just came to a shocking realization: I have never seen one statistical example in all of his writings!

What does that tell you?

Here is a wonderful example of his no-nonsense style in an excerpt from an email on which I was copied. Kerridge wrote it in 2000, but it is still relevant today:

“Or take the ‘Attack on the Quality Movement.’ As Ed Baker warns us, some of the attacks are justified. We do often concentrate too much on ‘quality tools,’ instead of ways to improve the whole system. This reminds me of another of [Deming’s] comments: ‘Don’t waste too much time on tools and techniques. You can learn the lot in 15 minutes.’

“It is easy to feel lost without concrete tools to hang on to. OK, so we need a bit more self-improvement. You have to crawl before you can walk, but you don’t want to spend your whole life crawling.

“I don’t wish to discourage anyone, not even myself. We can be so appalled by our own ignorance that we forget how much we have learned. Of course, if we think we know everything, we haven’t yet begun. Just as every process or system needs continual improvement, so does everyone’s understanding.

“Learning is fun. Focus on the joy of learning rather than the visible effect we have, and we will both enjoy it more, and achieve more, in the long run.

“Shewhart wrote, ‘Progress in modifying our concept of control has been and will be comparatively slow.’ By control in this context he meant, I believe, his whole approach, not just control charting, though that is a good place to start.

“The first thing we must learn is patience. This is difficult, in a world where there is so much pressure for short-term, visible results.

“One of the (many) reasons why the 14 Points are so important is that they create a world of long-term thinking, instead of short-term goals and pressures.

Organizational transformation makes individual transformation easier, which makes organizational transformation easier... in a never-ending cycle.”

Davis Balestracci


About The Author

David Kerridge

David Kerridge was the former head of statistics at Aberdeen University. An expert in W. Edwards Deming’s management philosophy, Kerridge wrote extensively about Deming’s work and was a leader in the British Deming Association.


A kind of humble wisdom

I had the privilege of trading e-mails with Dr. Kerridge for 10 years. He was always willing to help and teach and I learned a lot about statistics (and when not to use it) and Deming Management Philosophy. He deemed Walter Shewhart "one of the most profound thinkers of our time" and, many times, a simple debate on control charts operation was enriched by his knowledge of Information Theory, Systems Thinking, Systems Limits and Management. He used to give thanks for the questions I sent to him, from the simplest one to the most complex. His wisdom was surpassed only by his humility ("I wish I could learn faster").

Rest in Peace, my good friend.