Question

A sample with a sample proportion of 0.4 and which of the following sizes will produce the widest 95% confidence interval when estimating the population parameter?

A. 100
B. 75
C. 50
D. 150

Answer 1

C. 50

Explanation:

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

`\pi \pm z\sqrt{(\pi(1-\pi))/(n)}`

In which

z is the zscore that has a pvalue of
`1 - (\alpha)/(2)`.

The margin of error is:

`M = z\sqrt{(\pi(1-\pi))/(n)}`

The higher the margin of error, the wider an interval is.

As the sample size increases, the margin of error decreases. If we want a widest possible interval, we should select the smallest possible confidence interval.

So the correct answer is:

C. 50