Question

Within the first 24 hours of a heart attack, of the 691 subjects interviewed, 515 reported
Exposure to traffic before the heart attack.
A 95% confidence interval for the percentage of All heart attack victims exposed to traffic.
a. [.69, .81]
b. [.71, .79]
c. [.73, .77}

Answer 1

Solution :

Given that,

n = 691

x = 515

Point estimate = sample proportion = = x / n = 515/691=0.745

1 -   = 1- 0.745 =0.255

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z/2 = Z0.025 = 1.96   ( Using z table )

Margin of error = E = Z /2 * ((( * (1 - )) / n)

= 1.96 (((0.745*0.255) / 691)

= 0.0325

A 95% confidence interval for population proportion p is ,

- E < p < + E

0.745-0.0325 < p <0.745+ 0.0325

0.71< p < 0.79

(0.71, 0.79)

The 95% confidence interval for the population proportion p is :