The Mr. Potato Head simulation developed by Dr. Dave Williams (instructor notes available at Dave’s website www.truesimple.com) teaches people how to use Plan-Do-Study-Act cycles. Teams are challenged to build Mr. Potato Head as fast as possible so that the assembled toy matches a standard construct as judged by one team member using a three point scale. The last few times I have led the simulation, we used the standard shown at left.

The simulation teaches elements of testing changes to improve performance. It uses the basics of Plan-Do-Study-Act cycle as defined by the authors of The Improvement Guide and discussed in this blog post

Here’s how we pose the simulation aim to teams: Build Mr. Potato Head as fast and accurately as possible by the end of the simulation session.

The first build cycle typically takes 60 seconds or more with less than perfect accuracy, as shown by the record from one of our simulation sessions at left.

To run a second cycle, teams take Mr. Potato Head apart and prepare to build it again.

After the third cycle, a few teams may hit on the idea of not disassembling Mr. Potato Head at all, just having a Mr. Potato Head “ready to go.”

At the “3-2-1-go!” signal, a team using the idea of a “ready to go” Mr. Potato Head just presents the assembled toy to the inspector. Less than 1 second to have the task done.

The innovative teams reason this way:

If the purpose of assembling a Mr. Potato Head is to have a Mr. Potato Head that matches the photo, then just skip the disassembly to start from scratch and then skip the new assembly!

These teams demonstrate a fundamental engineering insight: the best way to improve an assembly operation is to eliminate the need for assembly entirely.

Shigeo Shingo codified this insight when he distinguished between process and operations analysis (discussed here)

Practical Application

A couple of hours after last week’s Mr. Potato Head simulation--part of an educational program for program managers at a federal agency--we had a real application of the fundamental engineering insight.

One of the project teams described an opportunity to improve a service request form. In the past, customers have filled out forms indifferently and inconsistently. The total number of customers is relatively small, about 20, though each customer may work through more than one request for service.

The improvement suggestion: eliminate the need for customers to fill out the form. Rather, have the service manager interview the customers and log the service requests directly so that services can be scheduled for delivery. No need to redesign the service request form and struggle to shape customer behavior.

The team is still considering the opportunity—the legacy form has a strong hold on their thinking and there are some practical issues to work out. Nonetheless, a small-scale test of the “eliminate the form” idea seems like a good idea.

Gerry Nadler’s General Design Perspective

Industrial engineer Gerry Nadler studied practices of effective planners and designers when he developed a theory of planning and design. In particular, effective designers know how to think about a flexible range of purposes. Nadler describes how to construct a hierarchy of purposes, from smaller to larger, to operationalize this design thinking.

Nadler shows that if you shift attention to a larger purpose relative to your original purpose, you open the door to creative and powerful designs. See G. Nadler (1981), The Planning and Design Approach, Wiley Interscience: New York, chapter 12 “Operational Details on Pursuing the P&D Approach”, pp. 135-142.


My API colleagues Lloyd Provost and Jerry Langley pointed me to a 2014 article by Anhøj and Olesen, “Run Charts Revisited: A Simulation Study of Run Chart Rules for Detection of Non-Random Variation in Health Care Processes” (PLOS One, http://dx.doi.org/10.1371/journal.pone.0113825).

Anhøj and Olesen look at the three run chart rules I reviewed in my post “Run Charts in Quality Improvement Work”, published 2 February 2015. They also offer useful guidance on run chart analysis as “Guidelines for Using and Interpreting Run Charts for Health Care Improvement.”

For the shift rule—number of consecutive values on one side of the median of a series of values—Anhøj and Olesen cite M. Schilling (2012), "The Surprising Predictability of Long Runs", Mathematics Magazine. 85, pp. 141–149 (available here). Schilling’s analysis leads to a simple formula for the number of consecutive values on one side of median that would be surprising, relative to series of independent realizations from a single probability distribution.

If you define n as the length of the original series, omitting any points that fall exactly on the median, the formula is: calculate log2(n) + 3 and then round to the nearest integer.

Using the simulation functions developed in R for my 2015 post, here’s the frequency of seeing 6, 7, 8 or 9 consecutive values on one side of a median for series of length n, n between 12 and 48.

Go to this GitHub repository for the R Markdown file that will produce the table shown here.

Restricting run chart analysis to series lengths less than n=20, the table shows that the rule “shift of six consecutive values on one side of the median” proposed by Perla et al. (2011) is a reasonable rule of thumb when looking for confirmation of improvement in short series.

While the Anhøj and Olesen rule doesn’t make sense for a series of length 12--the longest shift on one side of the median is six consecutive values—it looks like a reasonable guide for run chart analysis if you can estimate the critical value, which depends on a base 2 logarithm. For the range of n in the table, just linearly interpolate between powers of 2. E.g. for a series of length n=22, 22 is less than halfway between 16 and 32, so the quick estimate critical value is log216 + 3 = 7. When length of the series is halfway or more to the next power of 2, use the higher power of 2: E.g. for n=48, 48 is halfway between 32 and 64, so the estimate of the critical value is log264 + 3 = 9.

On the other hand, as Lloyd Provost noted last year, for series longer than n=20, a control chart often can provide more insight than a run chart. You can augment the Shewhart “3 sigma rule” with a shift rule based on Anhøj and Olesen, as these authors suggest in the Guidelines section of their paper.


On the first Sunday after the start of the school year, the Quaker Meeting I attend in Madison, WI has a pancake breakfast. The event marks the start of the new year’s First Day School for the Meeting’s children (Quakers traditionally use numbers for days of the weeks and months of the year—First Day is Sunday).

The aim of the pancake breakfast is actually to provide an experience for children and adults to work together to produce and share the meal. Children and a teenager or two pour dollops of batter onto the griddles, monitor the cooking, flip and serve. The adults are in the kitchen, mostly in support.

To cook and serve a few hundred pancakes in the 100 minutes between the end of first Meeting for Worship at 9:30 a.m. and the start of late Meeting for Worship at 11:15 a.m. takes organization and planning.

Bob Newbery, adult leader of the pancake team for 15 years, has implemented a key idea: convert internal set-up to external set-up.

Let me explain.

In pancake production, you assemble and combine a variety of dry and liquid ingredients.

Bob’s standard recipe at left shows that you start by combining the eggs and buttermilk, then add the sifted dry ingredients, followed by the melted butter. In most home settings, it is perfectly all right to proceed by combining the five dry ingredients, measuring out and sifting and then working through the recipe. This takes 10 minutes or more just to work with the dry ingredients, not counting the gathering and opening of containers, cleaning up inevitable spills, and putting things away.

So Bob converted the set-up of dry ingredients to make it "external" to our Quaker pancake cooking process. That is, the only set-up that needs to happen right before cooking on pancake breakfast Sunday is the combining of the wet and dry ingredients. That combining remains as "internal" set-up in our current production system.

Here's the external set-up:  All of the dry ingredients are premixed and assembled in plastic containers of the correct volume to correspond to the recipe. You can see a container of premixed and sifted dry ingredients ready to go in the blue-topped container at the start of this blog.

To prepare the batter takes less than four minutes, even less if the butter has been melted before mixing of ingredients begins. As the production bottleneck is the actual cooking of the batter on the griddles, people like me who are batter makers then can help the kids or wash dishes so that the kitchen is productive and cleaned up by noon. Given our production system, there’s no point of converting more internal set-up to external but as an exercise for the reader, what other set-up now internal could be converted to external?


Shigeo Shingo first distinguished the notion of internal and external set-up. He discussed this concept at length, along with many other insights in his book A Revolution in Manufacturing: The SMED System, Productivity Press, 1985, Cambridge, MA. SMED stands for “single minute exchange of die”, which enshrines the breakthroughs Shingo developed, culminating in the reduction in set-up time for a press at the Toyota Motor main plant in 1969 from hours to under 10 minutes--to single minutes, to change out the die set in the press.

Clinic Application:  The week before Pancake Breakfast, I observed young patients in a dental clinic receiving services. Good dental practice calls for application of sealants to permanent molars for kids with elevated risk for cavities.   The sealant process takes just a few minutes with a reasonably cooperative child. If the dental staff can provide this service while the patient is in the exam room (rather than needing to make a special additional appointment), that’s good for the patient and good for managing the clinic appointment schedule. To find the time for sealants during a standard exam appointment, applying the change concept "convert internal set-up to external set-up" can yield the minutes required.

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