In: Statistics and Probability
Assuming normality, construct the requested confidence interval.
A sociologist is interested in the age at which a mother has her first child. A random sample of 20 recent births yielded an average maternal age to be 30 years with a standard deviation of 6.2 years.
Construct a 99% confidence interval for the mean age at which a mother has her first child.
Question 17 options:
(27.10, 32.90) |
|
(26.43, 33.57) |
|
(27.28, 32.72) |
|
(27.60, 32.40) |
|
(26.03, 33.97) |
c )solution
Given that,
= 30
s =6.2
n = 20
Degrees of freedom = df = n - 1 = 20- 1 = 19
At 99% confidence level the t is ,
= 1 - 99% = 1 - 0.99 = 0.01
/ 2 = 0.01 / 2 = 0.005
t /2 df = t0.005,19 = 2.861 ( using student t table)
Margin of error = E = t/2,df * (s /n)
= 2.861* ( 6.2/ 20) = 3.97
The 99% confidence interval is,
- E < < + E
30 - 3.97< <30 + 3.97
(26.03, 33.97)