- September 23, 2005 at 8:53 pm #40803
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I monitor a test by running a standard each day and monitoring the results using an Xbar-R chart. I now have 20 subgroups, a total of 60 individual samples. I want to see how close the average is to the reference value for the standard. If I use the one sample t test:
X +/- t(sigma)/sqrt(n)
what should I use for the degrees of freedom and sigma? Based on the subgroup averages or the individual results? Or does it matter?
Thanks.0October 3, 2005 at 5:17 pm #127802
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