In: Statistics and Probability
When people smoke, nicotine is converted to cotinine, which can be measured. A sample of 40 smokers has a mean cotinine level of 172.5. Assuming that the standard deviation is known to be 119.5, find a confidence interval estimate of 90% of the mean cotinine level for all smokers. What aspect of this problem is not realistic?
Solution :
Given that,
Point estimate = sample mean = = 172.5
Population standard deviation =
= 119.5
Sample size = n =40
At 90% confidence level the z is
= 1 - 90% = 1 - 0.90 = 0.1
/ 2 = 0.1 / 2 = 0.05
Z/2 = Z0.05 = 1.645 ( Using z table )
Margin of error = E = Z/2
* (
/n)
= 1.645 * ( 119.5 /
40)
E= 31.0816
At 90% confidence interval estimate of the population mean
is,
- E <
<
+ E
172.5 - 31.0816 <
<172.5 +31.0816
141.4184 <
< 203.5816
( 141.4184 , 203.5816 )