Variance and Standard Deviation: Why divide by n-1?

See all my videos at www.zstatistics.com :) This video covers a few pesky concepts that are often glossed over. 0:00 Variance and standard deviation recap 2:39 Why do we bother with "variance" at all (ie. why square stuff)? 6:55 Why do we divide by n-1? 10:47 What do we mean by degrees of freedom? Spreadsheet downloadable here: http://www.zstatistics.com/s/Empirical-proof-of-standard-deviation.xlsx