What is a confidence interval

We have already established that a mean derived from a sample is unlikely to be a perfect estimate of the population mean. Since it is not possible to produce a single reliable value, a commonly used way forward is to quote a range within which we are reasonably confident the true population mean lies. Such a range is referred to as a confidence interval . 

The mean derived from the sample remains the best available estimate of the population mean and is referred to as the point estimate . We add and subtract a suitable amount to the point estimate to define upper and lower limits of an interval. We then state that the true population mean probably lies somewhere within the range we have now defined. 

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