This means that most men ( about 68 percent , assuming a normal distribution ) have a height within 3 inches of the mean ( 67-73 inches ) - one standard deviation - and almost all men ( about 95 % ) have a height within 6 inches of the mean ( 64-76 inches ) - two standard deviations .
A standard deviation of 3 '' means that most men ( about 68 % , assuming a normal distribution ) have a height 3 '' taller to 3 '' shorter than the average ( 67 '' -73 '' ) - one standard deviation .