Scatterplot


Scatterplot

A scatter graph or scatter plot is a type of display using Cartesian coordinates to display values for two variables for a set of data. The data is displayed as a collection of points, each having the value of one variable determining the position on the horizontal axis and the value of the other variable determining the position on the vertical axis. [Utts, Jessica M. "Seeing Through Statistics" 3rd Edition, Thomson Brooks/Cole, 2005, pp 166-167. ISBN 0-534-39402-7]

A scatter plot only specifies variables or independent variables when a variable exists that is under the control of the experimenter. If a parameter exists that is systematically incremented and/or decremented by the experimenter, it is called the "control parameter" or independent variable and is customarily plotted along the horizontal axis. The measured or dependent variable is customarily plotted along the vertical axis. If no dependent variable exists, either type of variable can be plotted on either axis and a scatter plot will illustrate only the degree of correlation (not causation) between two variables.

A scatter plot can suggest various kinds of correlations between variables with a certain confidence level. Correlations may be positive (rising), negative (falling), or null (uncorrelated). 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 (alternatively called 'trendline') can be drawn in order to study the correlation between the variables. An equation for the correlation between the variables can be determined by established best-fit procedures. For a linear correlation, the best-fit procedure is known as linear regression and is guaranteed to generate a correct solution in a finite time. Unfortunately, no universal best-fit procedure is guaranteed to generate a correct solution for arbitrary relationships.

One of the most powerful aspects of a scatter plot, however, is its ability to show nonlinear relationships between variables. Furthermore, if the data is represented by a mixture model of simple relationships, these relationships will be visually evident as superimposed patterns.

For example, to display values for "lung capacity" (first variable) and how long that person could hold his breath (second variable), a researcher would choose a group of people to study, then measure each one's lung capacity (first variable) and how long that person could hold his breath (second variable). The researcher would then plot 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 his breath for 21.7 seconds would be represented by a single dot on the scatter plot at the point (400, 21.7) in the Cartesian coordinates. The scatter plot of all the people in the study would enable the researcher 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 the two variables.

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.

ee also

* List of information graphics software
* [http://www.psychwiki.com/wiki/What_is_a_scatterplot%3F What is a scatterplot?]

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Scatterplot — Beispiel eines Streudiagramms, in dem die Länge und Breite von verschiedenen Artillerieschiffen dargestellt ist Ein Streudiagramm (engl. Scatterplot) ist die graphische Darstellung von beobachteten Wertepaaren zweier statistischer Merkmale. Diese …   Deutsch Wikipedia

  • scatterplot — scat·ter·plot (skatґər plot) a plot in rectangular coordinates of paired observations of two random variables, each observation plotted as one point on the graph; the scatter or clustering of points provides an indication of the relationship …   Medical dictionary

  • scatterplot — ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ noun Etymology: scatter (III) + plot : scatter diagram …   Useful english dictionary

  • Plot (graphics) — Scatterplot of the eruption interval for Old Faithful (a geyser). A plot is a graphical technique for representing a data set, usually as a graph showing the relationship between two or more variables. The plot can be drawn by hand or by a… …   Wikipedia

  • Seriation (archaeology) — In archaeology, seriation is a relative dating method in which assemblages or artifacts from numerous sites, in the same culture, are placed in chronological order. Where absolute dating methods, such as carbon dating, cannot be applied,… …   Wikipedia

  • Chart — For other uses, see Chart (disambiguation) , Graph (disambiguation) , and Diagram For information about charts in Wikipedia, see Wikipedia:Graphs and charts. A pie chart. A chart is a graphical representation of data, in which the …   Wikipedia

  • GeoDA — is a free software package that conducts spatial data analysis, geovisualization, spatial autocorrelation and spatial modeling. The package was developed by the Spatial Analysis Laboratory of the University of Illinois at Urbana Champaign under… …   Wikipedia

  • Mondrian (software) — Mondrian Developer Martin Theus Stable release 1.2 (January 11, 2011) OS Windows, Macintosh, Linux Website http://www.rosuda.org/Mondrian Mond …   Wikipedia

  • Ordinary least squares — This article is about the statistical properties of unweighted linear regression analysis. For more general regression analysis, see regression analysis. For linear regression on a single variable, see simple linear regression. For the… …   Wikipedia

  • List of graphical methods — This is a list of graphical methods with a mathematical basis.Included are diagram techniques, chart techniques, plot techniques, and other forms of visualization.There is also a list of computer graphics and descriptive geometry topics.imple… …   Wikipedia