By using the concept of confidence interval, it can be concluded that-
To reduce confidence interval, it is needed to increase sample size.
Option c is correct
What is confidence interval?
Suppose there is an unknown parameter whose range of estimate is required. Confidence interval gives the range of estimate of this unknown parameter.
Formula for percentage confidence interval
[tex]\bar{x} \pm z_\frac{\alpha}{2} \times \frac{\sigma}{\sqrt{n}}[/tex]
We have to reduce the size of the confidence interval
Confidence interval has no effect on mean, directly proportional to standard deviation and inversely proportional to sample size
So to reduce confidence interval, it is needed to increase sample size.
Option c is correct
To learn more about confidence interval, refer to the link-
https://brainly.com/question/15712887
#SPJ4
Complete Question
After constructing a confidence interval estimate for a population mean, you believe that the interval is useless because it is too wide. in order to correct this problem, you need to:
Select one:
a. increase the population standard deviation
b. increase the level of confidence
c. increase the sample size
d. increase the sample mean
e. none of these would help