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Trying to work out a 2/3 sigma failure rule on a selection of data points

lodey101

Community Trekker

Joined:

Oct 4, 2011

Hi there,

I was wondering if someone could help me out. I have a raw data pull and I would like to try to  manually work out if 2 out of the last 3 points is above 3 sigma. I already have worked out my control limits via control charts based on 4 pseudo screened data. If my UCL was 3.75 and I had the following values 2,3.9,4.2 (may not be in that order) then how would I be able to apply this rule to populate a variable to trigger the rule.

3 REPLIES
mewing

Community Trekker

Joined:

Jun 23, 2011

Try something like this:

n = N Row(:Data Table);

c = 0;

if(:Column > 3.75,c <- c+1);

if(:Column[n-1] > 3.75,c <- c+1);

if(:Column[n-2] > 3.75,c <- c+1);

if(c >= 2, [Do whatever you want as a response here]);

ms

Super User

Joined:

Jun 23, 2011

A condensed version of the same idea (utilizing element-wise comparison):

If( Sum( :Column[n - 2 :: n] > 3.75 ) >= 2, [Do whatever you want as a response here]);

lodey101

Community Trekker

Joined:

Oct 4, 2011

thanks