Chapter 19. Statistical Quality Control


Some statistics are for proving things. Some statistics are for discovering things. And some statistics are to keep an eye on things, watching to make sure something stays within specified limits.

The watching statistics are needed mostly in industry for systems of machines in production processes that sometimes stray from proper adjustment. These statistics monitor variation, and their job is to distinguish the usual random variation (called common causes) from abnormal change (called special causes).

These statistics are usually from a time series, and the patterns they exhibit over time are clues to what is happening to the production process. If they are to be useful, the data for these statistics ...

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