99% Confidence Interval 2011, standard, percent, normal

richer

Are 99% of all observations 3 standard deviations away from the mean or 2.58 standard deviations away?

I read somewhere that 99 percent of observations under a normal distribution will be +/- 3 standard deviations from mean, but the formula for the 99% confidence inverval of a normal distribution is mean+/- 2.58*std dev


Im confused!



Edited 1 time(s). Last edit at Sunday, May 15, 2011 at 11:13AM by adq123.