Scatterplot

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Waiting time between eruptions and the duration of the eruption for the Old Faithful geyser in Yellowstone National Park, Wyoming, USA.

A scatterplot or scatter graph is a graph used in statistics to visually display and compare two or more sets of related quantitative, or numerical, data by displaying only finitely many points, each having a coordinate on a horizontal and a vertical axis.

The scatter diagram is one of the seven basic tools of quality control, which include the histogram, Pareto chart, check sheet, control chart, cause-and-effect diagram and flowchart.

For example, if a statistician were studying the effects of lung capacity on the ability to hold one's breath, he would choose a group of people to study, and he would test each one's lung capacity (first data set) and how long that person could hold their breath (second data set). Then he would set up a scatter plot, assigning "lung capacity" to the horizontal axis, and "time holding breath" to the vertical axis. A person with a lung capacity of 400 cc who held their breath for 21.7 seconds would be represented by a single dot on the scatter plot at the point (400, 21.7) in Cartesian coordinates. The scatter plot of all the people in the study would enable the statistician to obtain a visual comparison of the two sets of data, and help him to determine what kind of relationship there might be between them.

Scatter Plot (or scatter diagram) shows the position of all of the cases in an x-y or x-y-z coordinate system. The relationship between interval variables can be identified from scatter graph. A dot in the body of the chart represents the intersection of the data on the x and y axis.

One advantage of a scatterplot is that it does not require a user to specify dependent or independent variables. Either type of variable can be plotted on either axes. Scatterplots represents the association (not causation) between two variables.

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