Question

(1) Is climate change causing more severe storms? In a 2017 pre-Hurricane Irma

survey, 486 out of 1,080 adults answered in the affirmative. In a 2017 post-

Hurricane Irma survey, 546 out of 1,050 answered affirmatively. Establish a 90%

Confidence interval estimate of the difference (pre- minus post-hurricane) between

the proportions of adults pre-Hurricane Irma and post-Hurricane Irma who believe

climate change is causing more severe storms.

Answer 1

90% Confidence Interval for difference in Proportion = (-0.106, -0.034)

Explanation:

The formula for difference in proportions is given as:

p1 - p2 ± z × √p1(1 - p1)/n1 + p2(1 - p2)/n2

p = x/n

In a 2017 pre-Hurricane Irma

survey, 486 out of 1,080 adults answered in the affirmative.

x1 = 486

n1 = 1080

p1 = 486/1080 = 0.45

In a 2017 post- Hurricane Irma survey, 546 out of 1,050 answered affirmatively.

x2 = 546

n2 = 1050

p2 = 546/1050 = 0.52

Z score for 90% confidence interval = 1.645

Confidence Interval

=0.45 - 0.52 ± 1.645 × √0.45 (1 - 0.45)/1080 + 0.52(1 - 0.52)/1050

= -0.07 ± 1.645 × √0.0002291667 + 0.0002377143

=-0.07 ± 1.645 × √(0.000466881)

= -0.07 ± 1.645 × 0.0216074293

= -0.07 ± 0.0355442212

Confidence Interval

-0.07 - 0.0355442212

= 0.1055442212

Approximately = -0.106

-0.07 + 0.0355442212

= -0.0344557788

Approximately = -0.034

Therefore, 90% Confidence Interval for difference in Proportion = (-0.106, -0.034)