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To: null and void

Three do show a trend. That’s always been a rule. Unless you are talking about something else.


34 posted on 10/17/2012 9:48:08 AM PDT by for-q-clinton (If at first you don't succeed keep on sucking until you do succeed)
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To: for-q-clinton
Nope.

For a symmetric data set (One where negative and positive numbers are possible) the rules are:

In no case do three or fewer points trigger an out of control alarm until you get beyond 2σ.

Three points define a plane to a mathematician, or a line to an engineer, but don't quite suffice for a trend under Western Electric control chart rules.

That being said, I start to watch a process very closely when three consecutive points are on the same area...

37 posted on 10/17/2012 10:03:02 AM PDT by null and void (Day 1366 of our ObamaVacation from reality - Obama, a queer and present danger)
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