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Statistical Techniques and 6 Sigma Uncertainity & Student's T distribution

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Author  Topic: Uncertainity & Student's T distribution 
sergiop Lurker (<10 Posts) Posts: 1 
posted 07 August 2001 02:18 PM
Hi! I'm trying to introduce calculus of uncertainity in my calibration procedures, but I'm not sure of what value of F (based on the Student's T distribution a number of degrees of freedom) must use: S1 = (SDEV / (N ^ 0.5)) * F I have a table (Guide to Expression of Uncertainty in Measurements), but reading some paper (Implementing ISO 17025 Measurement Uncertainity Requeriments in Software, Matt Nicholas, Fluke Corporation), they use half the values shown in the 95.45% column of the table What must I use? Entire value or half value of F to 95.45%?? Thanks  IP: Logged 
KenK Forum Contributor Posts: 16 
posted 09 August 2001 11:46 AM
I not sure I understand exactly what you are doing or what you want to do. I'm guessing you have calculated a mean, and want to provide a confidence interval  a measure of uncertainty. If that's the case, then the formula's are pretty simple: 95% confidence interval: mean +/ t[0.025,n1]*stdev/SQRT(n1) where t[0.025,n1] is a tvalue taken from a ttable. Sematech/NIST has a table at Find the column with 0.025 as the header and find n1 in the first column. If you're trying to do something else, please let us know. IP: Logged 
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