Proc ttest data =name h0 = μ 0 alpha = α The 95% confidence limits around the mean are We will test to see if the 1952 population from which the Dixon and Massey sample was gathered is statistically different, on average, from this recommended level. Many doctors recommend having a total cholesterol level below 200 mg/dl. Input Obs chol52 chol62 age cor dchol agelt50 $ Recall the data used in module 3 in the data file "dixonmassey." The general form for a confidence interval around the mean, if σ is unknown, isįor a two-sided 95% confidence interval, use the table of the t-distribution (found at the end of the section) to select the appropriate critical value of t for the two-sided α=0.05. We can also calculate a 95% confidence interval around the mean. Note: The shaded area is referred to as the critical region or rejection region. Using the significance level of 0.05, we reject the null hypothesis if |t| is greater than the critical value from a t-distribution with df = n-1. Using the significance level of 0.05, we reject the null hypothesis if z is greater than 1.96 or less than -1.96.