In: Statistics and Probability
an educational psychologist wishes to know the mean number of words a third grader can read per minute. She wants to make an estimate at the 99% level confidence. For a sample of 2006 third graders, the mean words per minute read was 27.2. assume a population standard deviation of 4.1. construct the confidence interval for the mean number of words a third grader can read per minute. Round your answer to one decimal place.
Solution :
Given that,
Point estimate = sample mean =
= 27.2
Population standard deviation =
= 4.1
Sample size = n = 2006
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
Margin of error = E = Z/2*
(
/
n)
= 2.576 * (4.1 /
2006 )
= 0.2
At 99% confidence interval estimate of the population mean is,
- E <
<
+ E
27.2 - 0.2 <
< 27.2 + 0.2
27.0 <
< 27.4
(27.0 , 27.4)