mean and standard deviation of a normal distribution
The standard deviation of a random variable, statistical population, data set, or probability distribution is the square root of its variance. It is algebraically simpler, though in practice less robust, than the average absolute deviation.his means that most men (about 68%, assuming a normal distribution) have a height within 3 inches of the mean (67â73 inches) â one standard deviation â and almost all men (about 95%) have a height within 6 inches of the mean (64â76 inches) â two standard deviations.