It’s More than Numbers: New Insights About Common and Special Cause Variation

By Dr. Doug Stilwell

Recently, in the middle of a difficult situation, it occurred to me that Understanding Variation (one of four pillars of the System of Profound Knowledge) isn’t simply about numbers plotted on a control chart. The concept of common and special causes can be applied to better help us understand situations where numbers don’t apply. It can provide us deeper knowledge of the reality we are experiencing. Allow me to share a recent personal experience that brought this to light for me.

My father, who was 91 years old and sadly passed away last May, had a severe foot infection since December. He had been in and out of the hospital and was receiving care in a facility for older adults. During his time there, my siblings and I went through a lot emotionally. His foot infection was so bad that it was clear it wouldn’t heal and would likely spread through his entire body. This situation took a toll on him physically, and it was an emotional roller coaster for my siblings and me.

There were many days when things looked really bad, and that was tough for us to handle. Then, unexpectedly, Dad would have a good day, and we would feel relieved and hopeful again. This pattern repeated multiple times, and it was emotionally draining for us.

One night, on my way home from visiting him, I had a sudden insight. While there were more bad days than good ones, we celebrated the good days with hopefulness as if they were the norm (common cause), when, in reality, they were exceptions (special cause). What I learned about variation is that it’s not just about numbers; it can apply to many situations; in our case, a highly emotional one.

Of course, when a family member’s health and life are at stake, emotions can be overwhelming. But understanding the difference between common (the bad days) and special cause (the good days) variation can help us manage our emotions better. We can still be grateful for the good days but recognize them for what they are – exceptions.

Our experience shows how variation and emotions are connected. By treating special cause events (good days) as common causes, our emotions were all over the place. Understanding this difference didn’t eliminate our emotions entirely, but it helped us navigate them more smoothly.

The power of understanding common and special cause variation goes beyond numbers. It can help us make sense of many experiences and, in difficult situations like what we experienced, can help us manage our emotional highs and lows as well as possible.

I dedicate this writing to my dad. Who knew, among the many things I learned from him over the course of my life, that he would deepen my understanding of variation!