# Standard deviation when sample is significant part of population

I know that sample standard deviation and population standard deviation are different, and are used in different cases (first when N>>n, second when N=n). But what when N>n, although not by much? For example, n=7 and N=30. I guess none of these two would be appropriate, but is there another formula for such cases? Or at least a rule of thumb saying which of these two would be more correct?

• See any number of posts relating to the finite population correction, such as here or here – Glen_b Jul 19 '14 at 7:50
• For certain statistics (such as the standard error of the mean) you'll see different formulas for samples coming from "Finite Populations". Namely, the usual formula multiplied by the sqrt((N-n)/(N-1)). Is this more along the lines of what you're asking about? – Steve S Jul 19 '14 at 8:12