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Margin of Error. Find the margin of error and the 95% confidence interval for the following studies. Briefly interpret the 95% confidence interval.According to Gallup a poll of 1012 people, 32% (about one-third) of Americans keep adog for protection.

Sagot :

The formula for determining margin of error for a population proportion is expressed as

[tex]\text{Margin of error = z}_{\frac{\varphi}{2}}\sqrt[]{\frac{p^{\prime}q^{\prime}}{n}}[/tex]

where

p' is the estimated proportion of success. It is also the point estimate

q' is the estimated proportion of failure

n is the number of people sampled

z alpha is the z score corresponding to a 95% confidence level

From the information given,

The success in this case is the proportion of Americans that keep a dog for protection. Thus,

p' = 32/100 = 0.32

q' = 1 - p' = 1 - 0.32 = 0.68

n = 1012

z alpha for a 95% confidence level is 1.96

Thus,

[tex]\text{margin of error = 1.96 x }\sqrt[]{\frac{0.32\times0.68}{1012}}\text{ }[/tex]

Margin of error = 0.015

The confidence interval is written as

margin of error ± margin of error

Thus, the 95 confidence interval is

0.32 ± 0.015

The lower limit is 0.32 - 0.015 = 0.305 = 0.305 x 100 = 30.5%

The upper limit is 0.32 + 0.015 = 0.335 x 100 = 33.5%

The interpretation would be

We estimate with 95% confidence that between 30.5% and 33.5% of Americans keep a dog for protection.