2.3. Variation and Statistics

In the previous section, we mentioned the following aspects of managing variation:

  • Identifying and quantifying sources of variation.

  • Controlling sources of variation.

  • Reducing sources of variation.

  • Anticipating sources of variation.

The first point, "Identifying and quantifying sources of variation," is a vital step and typically precedes the others. In fact, Six Sigma efforts aside, many businesses can derive useful new insights and better knowledge of their processes and products simply by understanding what their data represent and by interacting with their data to literally see what has not been seen before. Identification of sources of variation is a necessary step before starting any modeling associated with other Six Sigma steps. Even in those rare situations where there is already a high level of understanding about the data and the model, it would be very unwise to begin modeling without first investigating the data. Every set of data is unique, and in the real world, change is ubiquitous, including changes in the patterns of variation.

Given that the study of variation plays a central role in Six Sigma, it would be useful if there were already a body of knowledge that we could apply to help us make progress. Luckily, there is: statistics! One of the more enlightened definitions of statistics is learning in the face of uncertainty; since variation is a form of uncertainty, then the relevance of statistics becomes immediately clear.

Yet, statistics ...

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