Within each of these root causes, there are potential subroot causes.
A famous technique in the Toyota production system is known as the five
Why's. When you root cause problem solving, you
keep on asking why, why, why. The bag was too heavy.
Why? Well, there were too many pieces in there.
Why? Well, the machine that was putting the
pieces in was poorly calibrated. Why?
And so on, until you really get to the root cause.
Now, you notice, there's no rocket science involved in these diagrams, .
It's just a useful brain storming techniques.
If you draw nicer than I do, You notice that this little diagram looks
a little bit like a fish, With kind of the head of the fish up here,
And these being the fishbones. For this reason, this is also called a
fishbone diagram. Once you have mapped out the potential
root causes, you go into the field and start collecting data about the actual
defects. You'll then map out the defect
occurrences, or the number of defects for each of the types here in the Ishikawa
diagram for each of the defect types and that leads to a graph that looks like
this. So you sort them by number of occurrences,
we'll say too many pieces in the lead. And then all the way maybe having, you
know, just two problems where the bag was the root cause.
And then you can plug the cumulative number of problem occurrences in a curve
that looks like this. Typically, you'll find an 80-20 logic.
80% of the defects could be explained by twenty percent of the root causes.
This is known as a Pareto principle. Allow me to use the examples of the
Ishikawa diagram and the Pareto chart to make some philosophical reflections about
operations management. Most of what we do as academics, and most
of what we have done in this course, is create models of the underlying
operations. Now models are always an imperfect
approximation, a hopefully good approximation but they're still imperfect
approximation of the underlying reality in the operations.
Now as academics, consultants and managers, we're always at risk that the
ideas that we come up here are just based on our thoughts and models that we've
generated in our brain, but they don't work in reality.
What you have noticed with the problem solving in Kaizen is that there's a strong
emphasis on iteration between the world of reality and the world of thought.
The trigger for the improvement project is happening in the field when there are
defects. Because of G.
Doka, we stop the process, and start thinking about it.
This reflection is happening in the world of thought.
The Ishikawa diagram forces us to think about many root causes and that probably
will start triggering some improvement ideas.
But we don't just jump to the idea that we like.
Instead, we go back out in the field and collect data.
That's what the Pareto chart does. It's an empirical support for which root
cause we should go after first. Once we've identified the root cause that
accounts for the majority of the defects, we'll take that back into the world of
thought and start exploring some alternative solutions.
Christian TerwieschAndrew M. Heller Professor at the Wharton School, Senior Fellow Leonard Davis Institute for Health Economics Co-Director, Mack Institute of Innovation Management
