kabooze, if your sample just is the population of interest, then any figures describing the data will just be the population numbers. There would be no confidence intervals because, barring measurement error, there is no estimation or random error. A sample *estimator* is something we use to *infer* something about a population to which we think the sample represents. But if there is no difference between the representation and the actual population, then we *aren't making an inference*. We're simply *describing* the population. For instance, if we have a sample S of a population P, we can use the sample mean ES to estimate the population mean EP. In doing this, our point estimator will have error, and we set with a certain precision (confidence) the interval we think EP will reside in based on ES: i.e., with a certain confidence level we will expect EP to fall within a radius CI of ES. But if we're literally calculating EP itself, so that ES = EP, what CI is needed? None! We're not estimating, we're describing EP itself because S = P.