Once you encounter abnormal variation, or once you detect a defect, you have to start investigating the root causes. But how do you find the root cause? In this session, we'll introduce some truths for root cause problem solving. Specifically, we will introduce the concept of an Ishikawa diagram, as well as of as of a Pareto chart. Most of these tools belong to a toolbox known as Kaizen The idea of the Toyota production system is that quality and process improvement tasks don't have to be carried out by the management but are carried out by the front line employees. So our jobs is to put together a simple set of toolbox, so that we can equip with the front line workers to go about improving their work. Ishikawa diagrams are structured brainstorming techniques that help employees think about the root cause for a problem. Let's get back to our chocolate example. Maybe you want to figure out why the weight that we'll measure it for a particular set of bags or it's too heavy. Let's think about the potential root causes of this. One set of root causes might relate to their being too many. Pieces of chocolate in the bag. Another root cause might relate to each of the pieces being too heavy. Then in turn, it might have been the bag that was too heavy, or maybe the scale was broken, and the batch was of the right weight. And so we're struggling with a measurement problem. 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. Again, we're not gonna run out and standardized these solutions so quickly. We'll take it back on the field and run some small scale experiments. Only once we have done so can we standardize the process and say that's really a better process. So this oscillation between the world of thought. And reality, is the key signature of good problem solving. Rapid iteration is at the heart of creativity. Notice that both the Six Sigma production system, as well as the Toyota production system, emphasize this quick iteration between the world of thought and reality. Pareto charts and Ishikawa diagrams certainly look very simplistic, and almost trivial, compared to some of the material that we covered earlier on in this course. Remember when we computed the expected weight time, and the queue with M servers, the square root and the exponent there? But, don't hold the simplicity of the tool, of the Ishikawa diagram and the Pareto chart against them. To really drive Kaizen through your organization, you have to equip your frontline employees with simple frameworks. Both of these tools are emphasizing data collection in an empirical approach to problem solving, Very similar to statistical process control and six sigma. Instead of corporate BS, long PowerPoint presentations, we're going to follow the data to find the root cause behind the defect.
