In: Statistics and Probability
1. To estimate the mean triglyceride levels of people in West Palm Beach, a blood test on 30 randomly selected people was conducted and yielded a mean triglyceride level of 220, with a standard deviation of 12. Construct a 95% confidence interval for the true average triglyceride level of people in West Palm Beach. Round your answer to three decimal places.
solution
Given that,
= 220
s =12
n = 30
Degrees of freedom = df = n - 1 = 30- 1 = 29
At 95% confidence level the t is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
t /2,df = t0.025,29= 2.045 ( using student t table)
Margin of error = E = t/2,df * (s /n)
= 2.045 * (12 / 30) = 4.480
The 95% confidence interval estimate of the population mean is,
- E < < + E
220 - 4.480 < < 220+ 4.480
215.519 < < 224.481
( 215.519,224.481)