Is given value, a part of distribution
Is given value, a part of distribution
(OP)
Hello,
I have appx. 50 data points which were vibration measurements taken a month back. Now I have two data points measured recently. How do I statistically prove if the 2 recent values are also part of original distribution?
Thanks
SPM
Note: Being vibration measurement, the spec. is unilateral
I have appx. 50 data points which were vibration measurements taken a month back. Now I have two data points measured recently. How do I statistically prove if the 2 recent values are also part of original distribution?
Thanks
SPM
Note: Being vibration measurement, the spec. is unilateral





RE: Is given value, a part of distribution
Only when you get another 50 points of data can you realistically even begin to do some comparisons.
TTFN
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RE: Is given value, a part of distribution
» Frank.E.Grubbs, for example "Sample Criterion for Testing Outlying Observations", Annals of Math. Stat., vol 21, 1950, pp 27-58.
» W.J.Dixon. I have a photocopy of a paper by him titled "Analysis of Extreme Values", journal unknown, date unknown. He was at Univ of Oregon at the time. (This is not on "extreme values" in the sense that we now tend to use the term.)
» One of the above papers, Grubbs's I think, makes reference to work by a W.R.Thompson.
Most authors in this area caution that you should have a priori reason to suspect an observation to be an outlier before you subject it to outlier testing.
RE: Is given value, a part of distribution
RE: Is given value, a part of distribution
RE: Is given value, a part of distribution
A distribution with 2 samples does have a mean and standard deviation, after all. You just don't know what they are!
For instance if your 50 sample test had a mean of 5 and a standard deviation of 1, and your 2 extra sample had values of 2000 and 2001, without doing the maths you'd be pretty confident they were different.
Cheers
Greg Locock
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RE: Is given value, a part of distribution
RE: Is given value, a part of distribution
RE: Is given value, a part of distribution
My colleague calculated mean+4 sigma for the first set of 50 values and assumed that as UCL. When you compare the two new values with UCL, they are higher than UCL. So, he claims these two new values are not from the same distribution meaning it is an outlier.
But I am not fully convinced with this way. I think it is not proper statistical way. Also, when the distribution is skewed, I think my colleagues method will fail. But I did not have alternate suggestion. Now that I have Briby's way let me try this.
RE: Is given value, a part of distribution