Statistical Process Control
a.
Process and sampling distributions
i.
What is a sample?
1.
How many samples are possible given a population? (nCr)
2.
What does the distribution look like
a. A normal curve
b. Variation
i.
Variation is the enemy of quality… but some variation is
acceptable
1. Much around the mean, a little at the tails
3.
Would you expect any trends? (hopefully not)
ii. Would you believe the process was “stable”?
b.
In Control versus out of control
i.
The application of these sampling distribution principles to production
process is the basis for statistical process control (SPC)
ii. In control
1.
A process is in control when the process of variation is random and
within the limits of the normal curve. Or, variation is due to chance or
sampling error
2.
The process needs no adjustment
3.
If variation is due to sampling error… variation is statistical… and in
control
iii. Out of control
1.
A process is deemed out of control when the process variation is non
random or outside of the normal curve. This variation is due to some
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 Fall '09
 CAMP
 Statistics, Normal Distribution, Control Chart, variation

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