choosing the right improvement cycle: PDCA vs DMAIC

The PDCA cycle is just like the DMAIC cycle used to improve a process. therefore, it can sometimes be confusing to select the right cycle, even for an experienced person.  So how do you choose?

A first distinction that can be made is that the PDCA cycle is linked to lean while the DMAIC cycle is linked to six sigma. Therefore! if you want to reduce waste in your process, you can pick the PDCA cycle. While if you are looking to reduce variation, you can pick the DMAIC cycle.

PDCA cylce

Let's look at it in another way. the PDCA cycle is often used to improve in small steps. But do not worry! These small improvements can have cumulative a big impact on the business. 

The PDCA cycle is quite easy to learn, and can therefore be deployed quickly.

It is very efficient for small to medium-sized problems.

Due to its simplicity, The PDCA cycle is used more frequently for solving problems on a daily basis.

DMAIC cycle

On the other hand, the DMAIC cycle is used to improve in large steps.  Therefore the DMAIC process is often also referred to as break-through problem-solving. Due to the large step, there are often more resources needed when using the DMAIC process. 

The DMAIC process is more structured than the PDCA cycle. Therefore! it is more suited for complex problem-solving!

The DMAIC cycle heavy emphasis on data and statistical analysis. Due to this! The DMAIC process is more complex and less straightforward than the PDCA cycle. Therefore! It needs someone with the right six sigma skillset. This person will need to have a six sigma belt.

Problems are solved on a project basis with the DMAIC cycle.

Common Parent: the scientific method

To be honest, The cycles have a lot in common. This is normal since they have a common parent: the scientific method! The scientific method has 6 steps:

In the first step, you define the problem or make observations. For example. I want to know if water freezes faster when sugar is added.

In the second step, you formulate a hypothesis. The original hypothesis, also called the null hypothesis states that there will be no difference in freezing time between water with sugar added, and water without sugar. The alternative hypothesis is that there will be a difference in freezing time. 

In the third step, we gather appropriate data of the current process. How much sugar is normally added? How much sugar should we add to the water? Which temperature should we use? 

In the fourth step, we run an experiment. We fill two identical cups with the same amount of water and add the appropriate amount of sugar, that we have defined in the previous step. Now! We place the two cups in a freezer and measure the time of each cup to get completely frozen. I

In the fifth step, we can evaluate the results and create conclusions. In this case! the water with sugar added will take longer to freeze.

Finally, the sixth step:  Once we have gained this new knowledge we could start a new cycle to gain more knowledge. For example, we could add more or less sugar to see how it influences the freezing time. Or, we can add salt instead of sugar.

This sounds familiar, doesn’t it? The scientific method is used to continuously improve your knowledge! Just as the PDCA and DMAIC cycle have a similar approach to continuously improve your processes!

comparing the steps of the PDCA and DMAIC cycle

The “plan” phase of the PDCA cycle corresponds with the “define”, “measure” and “analyze” phase of the DMAIC phase. The “do” phase corresponds with the “improve” phase. And, The “check” and “act” phases correspond with the “control” phase.  Due to the similarity, you can use both techniques for improving a process! But, once you pick one you have to follow it to the end.

This article was updated on November 30, 2022