In: Statistics and Probability
Assume that a sample is used to estimate a population mean μ . Find the 99.9% confidence interval for a sample of size 811 with a mean of 56.8 and a standard deviation of 15.3. Enter your answer as a tri-linear inequality accurate to one decimal place (because the sample statistics are reported accurate to one decimal place).
ANSWER:
Given that,
Point estimate = sample mean =
= 56.8
sample standard deviation = s = 15.3
sample size = n = 811
Degrees of freedom = df = n - 1 = 811-1= 810
At 99.9% confidence level the t is ,
= 1 - 999% = 1 - 0.999 = 0.001
/ 2 = 0.001 / 2 = 0.0005
t
/2,df = t0.0005,24 = 3.492
Margin of error = E = t/2,df
* (s /
n)
= 3.492* (15.3 /
811)
= 1.9
The 99.9% confidence interval estimate of the population mean is
56..8 - 1.9 <
< 56.8 + 1.9
n mean is,
- E <
<
+ E
54.9<
< 58.7
99.9% C.I. = (54.9 , 58.7)
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