What are the two main types of variation described by Deming?

The two main types of variation described by Deming are common causes and special causes. Understanding these variations is crucial in the context of quality improvement as they help differentiate between the underlying factors affecting a process.

Common causes refer to the inherent variations that are always present within a system. These variations are due to the system's design and operational processes, thus affecting everyone involved in that system. They are the result of complex interactions among all the parts of the system and typically cannot be eliminated without changing the system itself. Understanding common causes is important for identifying areas where system-wide improvements can be made.

On the other hand, special causes are variations that are not inherent to the process. They arise from specific, identifiable factors that lead to unusual or unexpected output. These causes can often be eliminated with targeted interventions. Recognizing special causes allows organizations to address specific issues that may disrupt a consistent process and can lead to immediate improvements.

This distinction enhances a practitioner's ability to diagnose problems within a process and to choose the appropriate strategies for intervention and improvement. In summary, focusing on common and special causes empowers organizations to systematically enhance their quality by addressing both systemic and specific issues.