## Q. What is a confidence interval?

A confidence interval gives you a range of values that you believe the population parameter falls in.  Often you will be asked to find a $$100(1-\alpha)%$$ confidence interval, where $$1- α$$ is a quantity between 0 and 1 that represents the level of confidence. The confidence level is used to determine how often the true parameter falls within the confidence interval.  For example, if $$1-\alpha= 0.95$$ , you have a 95% confidence interval. This means that, if we calculate intervals for a large number of samples, the true parameter falls in approximately 95% of the intervals.