The 99 percent confidence interval for the mean score of all subjects lies greater than 63.464 and less than 78.936.
Given:
No. of samples (n)= 16
df = n-1 = 16 -1 = 15
The mean score is 71.2
The standard deviation = 10.5.
So, from the t-distribution of critical values table through the above-mentioned details. We get the values:
Alpha / 2 = 0.005
z = 99/100 + 0.005 = .99 + .005 = .995
Sample mean = xbar = 76.2
t = 2.947
The formula for standard error = E = value of t (at z, and df) / S.D./sqrt(n)
i.e. E = 2.947 x 10.5 / sqrt 16 = 7.736
I = 71.2 +/- E = Â 71.2 +/- Â 7.736
99 percent confidence interval - 71.2 +/- 7.736
Adding both sides 7.736 for range. We get,
63.464 < u < 78.936
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