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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, scatter diagram or scatter graph is a graph used in statistics to visually display and relate two numerical variables of a multidimensional data set by displaying the data as a collection of points, each having one coordinate on a horizontal and one on a vertical axis.

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

For example, to study the effects of lung capacity on the ability to hold one's breath, a statistician would choose a group of people to study, and determine each one's lung capacity (first variable) and how long that person could hold their breath (second variable). They would then set up the data in 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 variables in the data set, and help to determine what kind of relationship there might be between them.

A scatterplot does not require a user to specify dependent or independent variables. Either type of variable can be plotted on either axis. Scatterplots represent the association (not causation) between two variables.

A scatterplot can show various kinds of relationships, including positive (rising), negative (falling), and no relationship. If the pattern of dots slopes from lower left to upper right, it suggests a positive correlation between the variables being studied. If the pattern of dots slopes from upper left to lower right, it suggests a negative correlation. A line of best fit can be drawn in order to study the correlation between the variables. An equation for the line of best fit can be computed using the method of linear regression.

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