Predictability and Statistical Control

Predictability is an allimportant goal in science and engineering.
If the four underlying assumptions hold, then we have achieved
probabilistic predictabilitythe ability to make probability
statements not only about the process in the past, but also about
the process in the future. In short, such processes are said to
be "in statistical control".

Validity of Engineering Conclusions

Moreover, if the four assumptions are valid, then the process is
amenable to the generation of valid scientific and engineering
conclusions. If the four assumptions are not valid, then the
process is drifting (with respect to location, variation, or
distribution), unpredictable, and out of control. A simple
characterization of such processes by a location estimate, a
variation estimate, or a distribution "estimate" inevitably leads
to engineering conclusions that are not valid, are not supportable
(scientifically or legally), and which are not repeatable in the
laboratory.
