My first post on these forums, was referred here by a friend of mine. Thanks in advance! Mind that this question is coming from a BA in psych's worth of understanding: If I understand correctly, estimations of error margins are based on the relationship between a population and a sample of it. What has always confused me is that for a numerical relationship to be defined between these two variables, an integer must have been used for the population. If, for example, the population were considered to be infinite, then no sample of it could be said bear any resemblance to the infinite whole and thus no error estimations of the likelihood that it did could be made. So what I'm wondering, if I've understood the applied statistics correctly thus far, is how the likelihood that a sample is representative of the population from which it is drawn is ultimately determined without knowing the population size.