Originally Posted by mkaake

Just as a quick aside, it looks like you used Excel to figure out your standard deviation... but you need to use stdevp(), not stdev(). stdev() is only an approximation to standard deviation, whereas stdevp() is the calculated value. I think the only reason they provide both functions is for calculation time on very large data sets... but they should have made the more intuitive stdev() the real calculation, and not an approximation.