Sample sizes are never large. If N is too small to get a sufficiently-precise estimate, you need to get more data (or make more assumptions). But once N is «large enough,» you can start subdividing the data to learn more (for example, in a public opinion poll, once you have a good estimate for the entire country, you can estimate among men and women, northerners and southerners, different age groups, etc etc). N is never enough because if it were «enough» you'd already be on to the next problem for which you need more data.Gelman, Andrew. N.p… Web. 22 Jan 2013.
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