Understanding the Confounding Variable in Six Sigma

Last Updated on 13 September 2023

Simply put, a confounding variable is a third variable in a model that affects both the independent and dependent variables, thereby providing an alternate explanation for the observed relationship. It could introduce bias and make it difficult to determine the precise relationship between the variables of interest.

The Role of Confounding Variables in Six Sigma

Much like in other research, in Six Sigma, we seek to establish a cause-and-effect relationship between input (Independent Variables) and output (Dependent Variables). However, due to the complexity of the processes that we encounter, there are numerous factors that might alter the results of our study. These can be erroneously overlooked, leading to an incorrect cause-and-effect conclusion. This is where the confounding variables come into play.

Example of Confounding Variable

Consider a Six Sigma project aimed at reducing the time taken to serve customers at a restaurant. A team may identify the number of waitstaff as the independent variable affecting service time (the dependent variable). They may observe that increasing the number of waitstaff reduces the service time.

However, if they overlook the confounding variable – customer traffic, their analysis may be skewed. Customer traffic can impact both the number of waitstaff and the service time. Therefore, not considering this variable might lead to incorrect conclusions about the effect of waitstaff numbers on service time.

Importance and Impact

Confounding variables can greatly impact the validity of a Six Sigma project if not identified accurately. They can lead to expensive, time-consuming process adjustments, and incorrect assumptions that do not achieve the desired improvements. Therefore, it’s fundamental to identify, understand, and control confounding variables during the Define, Measure, Analyze, Improve, and Control (DMAIC) process.

Conclusion

Understanding the concept of confounding variables and handling them appropriately is essential for the accuracy and efficiency of your Six Sigma projects. As you advance through your Six Sigma journey, become more diligent at identifying these hidden variables for successful project outcomes.