A normal distribution is an idealized view of the world, producing the familiar, symmetrically shaped “bell-shaped curve.” It is usually based on a large set of measurements of one quantity—such as weights, test scores, or height—which are arranged by size. In a normal distribution, more than two-thirds of the measurements fall in the central region of the graph; about one-sixth of them are found on either side. Many of us are familiar with the normal distribution from standardized school test scores, as most result in a bell-shaped curve, with students hoping to at least fall in the middle of the curve.