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Suppose you had been in charge of designing the study. What sample size would be needed to construct a margin of error of 2% with 95% confidence

Sagot :

Answer:

A sample size of 2401 is needed.

Step-by-step explanation:

In a sample with a number n of people surveyed with a probability of a success of [tex]\pi[/tex], and a confidence level of [tex]1-\alpha[/tex], we have the following confidence interval of proportions.

[tex]\pi \pm z\sqrt{\frac{\pi(1-\pi)}{n}}[/tex]

In which

z is the z-score that has a p-value of [tex]1 - \frac{\alpha}{2}[/tex].

The margin of error is given by:

[tex]M = z\sqrt{\frac{\pi(1-\pi)}{n}}[/tex]

95% confidence level

So [tex]\alpha = 0.05[/tex], z is the value of Z that has a p-value of [tex]1 - \frac{0.05}{2} = 0.975[/tex], so [tex]Z = 1.96[/tex].

What sample size would be needed to construct a margin of error of 2% with 95% confidence?

This is M for which n = 0.02.

Supposing we have no estimate for the true proportion, we use [tex]\pi = 0.5[/tex].

[tex]M = z\sqrt{\frac{\pi(1-\pi)}{n}}[/tex]

[tex]0.02 = 1.96\sqrt{\frac{0.5*0.5}{n}}[/tex]

[tex]0.02\sqrt{n} = 1.96*0.5[/tex]

[tex]\sqrt{n} = \frac{1.96*0.5}{0.02}[/tex]

[tex](\sqrt{n})^2 = (\frac{1.96*0.5}{0.02})^2[/tex]

[tex]n = 2401[/tex]

A sample size of 2401 is needed.