Since we have a very small sample size (n=6) we should use the t-distribution, with df = n-1 = 5. So the critical t-stat for an 80% confidence interval is given by the cdf of the t distribution at 0.9 (1-alpha/2):
t.inv(0.9, 5) = 1.476 to 3 decimal places.
Mar 9th, 2015
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