In: Statistics and Probability
A lab tested the ibuprofen content in a drug manufacturer’s headache pills. After testing 500 random samples, the mean ibuprofen content was found to be 202 mg with a standard deviation of 10 mg. Construct a 99% confidence interval for the true mean ibuprofen content in all of the manufacturer’s headache pills.
Solution :
Given that,
Point estimate = sample mean = 
= 202
Population standard deviation =   
=  10
Sample size = n =
At 99% confidence level the z is ,
  = 1 - 99% = 1 - 0.99 =
0.01
/ 2 = 0.01 / 2 = 0.005
Z
/2
= Z0.005 = 2.576   ( Using z table )
Margin of error = E = Z
/2*
(
/n)
= 2.576* ( 10 / 
500)
= 1.1520
At 99% confidence interval estimate of the population mean is,
-
E < 
 < 
 + E
202-1.1520 < 
 < 202+1.1520
200.8480< 
 < 203.1520
(200.8480,203.1520)