The normal distribution. In a normal distribution, the most frequent observations fall near the mean and the least frequent observations occur farther away from the mean. The dark blue areas represent one standard deviation from the mean and account for 68.3 percent of all data. The medium and dark blue areas combined represent two standard deviations from the mean and account for 95.5 percent of all data. The light, medium, and dark blue areas combined represent three standard deviations from the mean and account for 99.7 percent of all data. The remaining small amount of data fall outside of three standard deviations. (a) Data that have a wide distribution have a large standard deviation. (b) Data that have a narrow distribution have a small standard deviation.