Friday, January 11, 2008

Sample vs. Population

Use English letters for sample statistics and Greek letters for the analogous population stat.

Sample stats typically use (n-1) for the sample size while population stats use N. The reason for this difference is beyond the scope of this class (at least for now).

The exception is the mean where both use n (and N).


lowkeydad said...

so... Excel always does the covariance function as if it is dealing with an entire population rather than a Sample. Therefore, I guess we need to be careful using Excel's built-in functions.

Eliezer said...

Yeh, it's kinda weird that way. For variance and standard deviation, the default is to consider the data a sample. There are alternative functions (varp and stdevp) to consider populations. But for some reason covar is for a population by default. To get covar for a sample take covar*n/n-1.