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radar
2006 Jan 04
4
Discrepency between confidence intervals from t.test and computed manually -- why?
I am sure there is something simple here I am missing, so please bear
with me.
It concerns the computation of the confidence interval for a population
mean.
The data are 125 measurements of Cs137 radation, a sample data set from
Davis "Statistics and Data Analysis in Geology" 3rd ed. (CROATRAD.TXT)
------------------
method 1: using textbook definitions: mean \pm se_mean * t-value
mu <- mean(Cs137); n <- length(Cs137)
se.mean <- sqrt(var(Cs137)/n)
# two-tail alphas
alpha <-...