Can anyone explain to me the difference between standard deviation and pooled standard deviation. How do I calculate the second one?

Question

joannablackwelder · Answer

I've never done it before but here is the formula :) http://stattrek.com/statistics/formulas.aspx

joannablackwelder · Answer

Standard deviation. Use this formula when the population standard deviations are known and are equal.

joannablackwelder · Answer

Pooled standard deviation. Use this formula when the population standard deviations are unknown, but assumed to be equal; and the samples sizes (n1) and (n2) are small (under 30).

joannablackwelder · Answer

http://stattrek.com/estimation/difference-in-means.aspx?tutorial=stat