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Intersection of two normal distributions 2

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Robbyod

Robbyod

Industrial
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May 11, 2010
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Hi all,
I am trying to find formulae for calculating the overlap between two normally distributed populations.
There are some online calculators specifically for this but they do not have the resolutinion i require.

So for M1,?1 and M2,?2, (where M is Mean and ? is StDev) what formula will give me the probability of samples from these populations overlapping.

Im trying to find the % interferance fit between an OD and ID

I have been using JMP so far as a stop gap but i know this is not entirely accurate, the method below is what im using

by finding the % of Group 2 below the point M1+3(?1) and vise versa, then multiplying the two %

M+3(?) still leaves 0.15% of the population unacounted for and i want a more accurate result.

Your comments on a better fast method aswell as the formuala are welcome and appraciated

Thanks
 
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Seems to me that you should red-flag this posting and repost in a more obvious forum forum1103. Have you even done a search?

TTFN

FAQ731-376
 
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I think it's a legit question for this forum. I wasn't aware of the one on Drafting Standards and that doesn't sound like a good fit to me.

I'd be tempted to start with something like a 2 sample t-test with the data.
 
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The OP's question pertains to "% interferance fit between an OD and ID" which seems to be a tolerancing problem.

TTFN

FAQ731-376
 
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While the underlying issue is a tolerance issue, the question and its specifics are statistical, which is why i chose this forum.

So, does anyone have any ideas?
 
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Thanks guys, what i did in the end was create an excel template which will calculate the % overlap of two data sets which can be pasted in.

Much easier than running through differential equations.

The template is giving me almost identical answers to the estimations i made with JMP (identical down to 2 decimals)

It will calculate the overlap between the two points 3 sigma from the mean in each population so there is still a minute % unnacounted for.

The template is attached below if anyone would like to use it.

 
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Sorry, the file attachment function doesnt seem to be working
 
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