Statistical Analysis Question: Confidence Intervals
Statistical Analysis Question: Confidence Intervals
(OP)
Hi all,
I have 26 data points I'd like to form a confidence interval around (i.e. points to bound the sample data and possibly the population data).
I can use a t-distribution type: mean +/- [sample/root(# data points)]*t_%5, but it doesn't fully capture the data points.
OR
I can use: mean +/- 3sigma, which does capture the data.
So I'm confused about the difference between the first and the second method.
I'd appreciate some help explaining this.
Cheers
I have 26 data points I'd like to form a confidence interval around (i.e. points to bound the sample data and possibly the population data).
I can use a t-distribution type: mean +/- [sample/root(# data points)]*t_%5, but it doesn't fully capture the data points.
OR
I can use: mean +/- 3sigma, which does capture the data.
So I'm confused about the difference between the first and the second method.
I'd appreciate some help explaining this.
Cheers





RE: Statistical Analysis Question: Confidence Intervals
RE: Statistical Analysis Question: Confidence Intervals
Something I'm realizing the more I read about CI, is they don't bound individual data points of a sample, but rather bound the mean of a sample.
So I want to bound data points of any sample.
RE: Statistical Analysis Question: Confidence Intervals
I suggest you read the Wikipedia articles on the subject:
http://en.wikipedia.org/wiki/Student%27s_t-distrib...
http://en.wikipedia.org/wiki/Confidence_interval
TTFN
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RE: Statistical Analysis Question: Confidence Intervals
A confidence interval or confidence bounds are not for individual data points of a sample.
The CI is for a samples mean only and says nothing with regard to the scatter range in a sample.
Maybe I need to look into sample variation (not variance) analysis......
RE: Statistical Analysis Question: Confidence Intervals
That's not strictly true. They bound the distribution of a PDF that best fits the data. Therefore, if your data is consistent with the PDF you are applying, then the CI will be consistent with those data points. When you calculate a standard deviation or variance, you make explicit assumptions about the data you are fitting, and if those assumptions are incorrect, then the variance could be drastically different than what it might be.
TTFN
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RE: Statistical Analysis Question: Confidence Intervals
RE: Statistical Analysis Question: Confidence Intervals
Example: Your product will meet the 50% confidence interval with a tolerance of +-.001.
But after you have the data, post manufacturing, it is only used to describe the distribution.
Since you have your data points all you can do is use the confidence interval to describe the distribution to show it does or does not meet requirements.
RE: Statistical Analysis Question: Confidence Intervals
another day in paradise, or is paradise one day closer ?
RE: Statistical Analysis Question: Confidence Intervals
That is what I ended up doing. Setting a t-CI specifically for the points around 3sigma from the sample mean.
RE: Statistical Analysis Question: Confidence Intervals