Refers to a statistical data distribution pattern. Certain data, when graphed as a histogram (data on the horizontal axis, amount of data on the vertical axis), creates a bell-shaped curve known as a normal curve, or normal distribution. Normal distributions are symmetrical with one central peak at the mean (average) of the data. The contour of the curve is bell-shaped. The spread of a normal distribution is determined by the standard deviation. The smaller the standard deviation, the more concentrated the data.