Two voting districts, C and M, were sampled to investigate voter opinion about tax spending. From a random sample of 100 voters in District C, 22 percent responded yes to the question "Are you in favor of an increase in state spending on the arts?" An independent random sample of 100 voters in District M resulted in 26 percent responding yes to the question. A 95 percent confidence interval for the difference

Step-by-step explanation:

Confidence interval for the difference in the two proportions is written as

Difference in sample proportions ± margin of error

Sample proportion, p = x/n

Where x = number of success

n = number of samples

For district C,

x = 22

n1 = 100

p1 = 22/100 = 0.22

For district M,

x = 26

n2 = 100

p2 = 26/100 = 0.26

Margin of error = z√[p1 (1 - p1) / n1 + p2 (1 - p2) / n2]

To determine the z score, we subtract the confidence level from 100% to get α

α = 1 - 0.95 = 0.05

α/2 = 0.05/2 = 0.025

This is the area in each tail. Since we want the area in the middle, it becomes

1 - 0.025 = 0.975

The z score corresponding to the area on the z table is 1.96. Thus, the z score for the confidence level of 95% is 1.96

Margin of error = 1.96 * √[0.22 (1 - 0.22) / 100 + 0.26 (1 - 0.26) / 100]

= 1.96 * √0.00364

= 0.12

Confidence interval = (0.22 - 0.26) ± 0.12

= - 0.04 ± 0.12