Everyone has their own favorite graph type or visual tool. I’m not ready to declare this 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.
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If you’re not familiar with them, we put out a great blog at Minitab to explain what they are and how to build one. In a nutshell, they are control charts that help analyze a process before and after an improvement, monitoring not only the change but how the process means and variability changed because of the improvement. This gives extra insight, not only into the improvement’s effect but also as to whether it’s part of a stable process (and sustainable).
Now that you’re familiar with the utility of before/after control charts, here are four ways you might want to use this type of visualization.
1. Capture the effect 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.
2. Capture the effect 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 the Covid pandemic, during it, and after are all extremely different. Highlighting this change can help explain the significant changes in the business.
3. Highlight improvements in patient experiences or patient care
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.
4. Monitor the performance of equipment
This could be done either after improving or to measure the effect of wear or lack of service over time. Factory equipment is expensive and critical to operations. Adjusting or fixing equipment can boost productivity and can be easily displayed using a before/after control chart. Staged control charts can even be useful to measure the effect 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.
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”).
You can see such statistical software at Minitab 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 meet necessary assumptions, and to interpret the results of your chart.
Published April 25, 2024, in the Minitab blog.
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PuMP Blueprint
Readers may also want to check out Stacey Barr's PuMP Blueprint program for implementing continual improvement. We found it to be very useful in our Production Department.
The Process Behavior Chart is covered in Step 6.
https://www.staceybarr.com/about/pump/
https://www.staceybarr.com/products/pumpblueprintworkshop/
Check out Stacey's interview with Dr. Donald Wheeler on interpreting signals from KPIs.
https://www.staceybarr.com/measure-up/interview-donald-wheeler-on-interpreting-signals-from-our-kpis/
Automating Process Changes in Control Charts
QI Macros Process Change Wizard will automatically identify process changes (trends and runs) and adjust the chart for you.
Stacy Barr and Donald Wheeler
Stacy Barr and Donald Wheeler make a winning team. Stacy lays the groundwork to develop KPIs in a thoughtful manner that will be meaningful, get accepted and used by management to align performance measures to strategy assuring right actions are taken to reach targets. She uses process behavior charts but instead of having red lines for the natural process limits she uses a light blue area fill to color between the natural process limits. This is much more impactful to the eye and makes it easier to tell a story about the usefulness of process behavior charts. Kudos to her for this advancement. We are considering adding this to our Process Behavior Charting Excel AddIn called http://www.PBCharts.com
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