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...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 <- c(1, 5, 10, 20)/100 # t-values for each tail t.vals <- qt(1-(alpha/2), n-1) # name them for the respective alpha names(t.vals) <- alpha # low and high ends of the confidence i...