4 Ways to Measure Improvement Using Before/After Control Charts with Stages

Joshua Zable | 4/25/2024

Topics: Featured Article, Control Charts

Everyone has their own favorite graph type or visual tool. I’m not ready to declare this one my favorite yet, but this oldie but goodie has got to get more time and attention. That’s right: I’m talking about Control Charts with Stages, also sometimes called Before/After Control Charts.  

If you’re not familiar with it, we put out a great blog explaining what they are and how to build one in Minitab. In a nutshell, they are control charts that help analyze a process before and after an improvement, monitoring not only the change but also how the process means, and variability changed because of the improvement. This gives extra insight, not only into the improvement's impact, but also as to whether it is part of stable process (and sustainable). 

Now that you’re familiar with the utility Before/After Control Charts, here are 4 ways you might want to use this type of visualization:


1. Capture the impact of An IMPROVEMENT

Imagine you’re charged with reducing the cycle time (i.e. the total time a production team spends on producing a single unit), to enable faster production to increase capacity to meet rising demand for your product. You embark on an improvement project and after you make changes you measure your success. A staged control chart is a great way to highlight the benefits of your improvement project. 

Control chart for impact of improvement


2. Capture the impact of a change in a business environment

Businesses are dynamic and constantly changing. Some of these changes are external forces, like competitor actions or a change in the operating environment, and some can be because of a strategic shift (this is why SWOT analyses are so popular, but I digress). Imagine you were a manufacturer of hand sanitizer and you needed to forecast the demand for your product. Your experience before COVID, during COVID and after are all extremely different. Highlighting this change can help explain the significant changes in the business. 

control chart with stages for hand sanitizer production



In this healthcare case, highlighting the improvement is critical for both practitioners and patients. Whether it’s physicians tracking therapies or a facility tracking improvements, not only do they wish to understand them, but they want to clearly communicate the benefits to patients. You can read about  how a hospital might track a key metric like reducing admission times (in the previously mentioned blog) or how it can be used to communicate the potential benefits of surgery. 



This could be done either after improving or to measure the impact of wear or lack of service over time. Factory equipment is expensive and critical to operations. Adjusting or fixing equipment can result in boosted productivity and can be easily displayed using a before/after control chart. Staged control charts can also be particularly useful even to measure the impact of normal maintenance. Read about a great example of someone measuring a car’s gas mileage to see if the service maintenance kept the performance consistent. 


Using Minitab for Ongoing Improvements 

As you can tell, control charts are simple but very powerful tools that can help you determine whether a process is in control (meaning it has only random, normal variation) or out of control (meaning it shows unusual variation, probably due to a "special cause").  

And when you use Minitab Statistical Software, you can choose Assistant > Control Charts... and get step-by-step guidance through the process of creating a control chart, from determining what type of data you have, to making sure that your data meets necessary assumptions, to interpreting the results of your chart. 


Ready to see what you can do with your data? 

Start Free Trial