In this chapter, we’ll discuss the DMAIC methodology and how that relates to the PDCA cycle. DMAIC is a five-step process, we start with Define. This involves really understanding issue we’re trying to address determining the outcome we want to accomplish. From there, we need to measure and determine the inputs and the things we can measure and potentially improve. Then we analyze and determine the best actions to implement the next step, which is to improve the process. Then we move on to Control. During this step, we make sure we achieve the results. We use that information as an input to the next iteration of the DMAIC process, and we start all over again. In contrast to DMAIC, the Plan, Do, Check, Act, or PDCA cycle is very similar, but a bit simpler. The Plan and Do steps correlate very much with Define, Measure, and Analyze. And then the Check and the Act correspond with Improve and Control. And making sure that we actually get the result that we’re seeking. The similarity is that both of these are intended to be cycles of continuous improvement. And neither is wrong or right, they’re just different and helpful to us in the practice of Six Sigma. Now we will discuss the Transfer function and how it plays into Six Sigma. And it starts with understanding the meaning of the letter Y in the equation. The Y represents the output, the result, the actual process that we want to improve, or the outcome.
The Six Sigma process takes inputs, applies a transformation, and produces outputs. In the function used here, X is the input, f is the transformation applied and Y is the output. These are the variables that actually contribute to the success of the process. The f or the function of X gives you the Y result. Another way of thinking about this is that the X inputs go through the f function of transformation, generating the outputs or the Y value. Now we will talk about the transfer function and how that relates to DMAIC. For example, let’s just say we’re going to call technical support to address a problem with our computer. This is the Define step of DMAIC. When we call, a series of things are going to happen. Let’s say that the Y in the transfer function represents how long it takes for you, a customer, to get the answer to your question. Now let’s identify the X factors. These are the various steps that will take place through the entire call to resolve the technical question. These also represent the Measure step of DMAIC. Once we have all those measures, we move on to Analyze and determine which are the critical few factors that make up most of the time. And what is the normal variation of that range of time? Then we determine what we can do to add efficiency and to shorten the amount of time to resolve the customer’s issue.
Once we’ve done that, we can move to the Improve phase and actually implement the counter measures and changes. From there, we move to the Control step of DMAIC and verify that the Y in the transfer function was improved. If you remember, the Y is how long it takes for the customer to get their answer to their question. Then we measured it with the X’s. Then we moved through the analysis and the function. We actually improved the value of Y by applying the steps of DMAIC. Since this is continuous improvement, we can go through the process repeatedly. This simple five-step process is very powerful if we’re willing to follow the rigor of Six Sigma. There are other improvement methodologies that we can leverage in the practice of Six Sigma. Statistical process control is one of these in which we have upper and lower control limits. We monitor processes to determine if and when they go out of control. And we use that to trigger root cause analysis and improvement. Statistical process control tools can actually trigger cycles of DMAIC to improve a process. We also have variance and defect reduction tools, correlated with total quality management, or TQM. These can be very helpful in analysis and improving processes. This is part of the Analyze-and-Improve steps of the DMAIC cycle. Another improvement methodology is teamwork, and the notion of quality circles. This concept was developed by Toyota. And it aimed at a team based approach to leveraging the DMAIC methodology, along with statistical tools and variance reduction tools like those that we’ve just discussed.