Question

What is the difference between common variation (also known as a natural variation) and assignable variation (also known as a special variation).

Answer 1

A common variation is also known as natural variation fluctuation, which is due to some unknown factors resulting in a steady but random distribution of output around the average of the data. The common variation is the measure of the process potential.

Examples of common variations

• poor working conditions,
• measurement errors,
• normal wear and tear,
• computer response times

An assignable variation is also known as special variation. which is due to the distribution of non-random results caused by a single identifiable factor with clearly defined characteristics. Such a circumstance is imminently manageable.

Relating to project management is if machine malfunctions, computer crashes, there is a power cut, etc. These type of random things that can happen during a project are examples of special cause variation.