Q. Why should I find a confidence interval instead of only using a hypothesis test?
The advantage of a confidence interval is that it gives you a range of possible values and provides a measure of variability. A hypothesis test only looks for statistical significance. For example, you could run a hypothesis test to determine if the mean for a given variable is zero. If the test is significant, you still don’t know any information about the true mean other than it isn’t zero. If you fit a confidence interval, then you would have a range of values that you are reasonably confident the true mean will fall into. You can also use the confidence interval to evaluate a hypothesis test. Continuing with the above example, if the confidence interval did not include zero, you would reject the statement that the mean is equal to zero.