Question

How to Calculate confidence intervals

Answer 1

To calculate confidence interval:

1. First determine the confidence level. Then find the appropriate z value.

For ex.

Confidence level	z value
80%	1.28
90%	1.645
95%	1.96
99%	2.576

2. Once this is done, we find sample mean and standard error

standard error can be population standard deviation or sample standard deviation/sqrt(sample size)

3. Lower level of confidence interval = sample mean - z*standard error

and upper level of confidence interval = sample mean + z*standard error