bubble plot
a graphical representation of data that is similar to a scatterplot but includes an additional third variable whose values are represented by differently sized circles. For example, a researcher might use a bubble plot to show the relationship between income, years of education, and age within a particular profession. The first two variables would be arrayed along the horizontal x-axis and vertical y-axis, respectively, with circles placed in the graph to indicate points of intersecting values; the radius of each circle would correspond to values of age, with larger circles indicating greater age.