In: Statistics and Probability
Proportion Problem. Each year Delta Dental does a survey of parents concerning the tradition of the Tooth Fairy. A random sample of 1,058 parents were asked about how much money they leave for a tooth and questions concerning how their child responded to the concept of the Tooth Fairy. In one question, 508 parents indicated that their child saved the money they got for their tooth.
You are asked to calculate a 99% Confidence Interval for this proportion.
.5 is contained in your confidence interval. This is a true or false question
Solution :
Given that,
n = 1058
x = 508
Point estimate = sample proportion = = x / n = 508/1058=0.48
1 - = 1 - 0.48=0.52
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 * (( * (1 - )) / n)
= 2.576 (((0.48*0.52) / 1058)
= 0.0396
A 99% confidence interval for population proportion p is ,
- E < p < + E
0.48 - 0.0396< p <0.48 + 0.0396
0.4404< p < 0.5196
The 99% confidence interval for the population proportion p is : (0.4404 , 0.5196)