A graph consisting of points whose coordinates represent values of data, often used to illustrate a correlation between one or more variables and a test group. See the illustration. Also called: point chart, point diagram. Or scattergram; Diagram whose purpose is to establish whether or not a relationship or correlation exists between two variables; for example, between life expectancy and gross national product. Each observation is marked with a dot in a position that shows the value of both variables. The pattern of dots is then examined to see whether they show any underlying trend by means of a line of best fit (a straight line drawn so that its distance from the various points is as short as possible).