One of the most important types of statistical distributions of data is the normal distribution. A normal distribution is defined by its mean and standard deviation. The following graph shows examples of normal curves.

The blue, red, and yellow curves all have a mean of 0, while the green curve has a mean of -2. The blue curve has a standard deviation of 0.2, the red curve has a standard deviation of 1.0, the yellow curve has a standard deviation of 5.0, and the green curve has a standard deviation of 0.5.

\fA normal distribution 2.35% 2.35% 13.5% 34% 34% 13.5% U -30 4-20 4-0 Uto u+20 1+30 68% of the data 95% of the data 99.7% of the data