A scatterplot (also called a scatter chart, scatter diagram or scatter graph [Wikipedia]) is a diagram in which the values of two metric variables are applied to the horizontal and vertical axes of a cartesian coordinate system. The resulting point in the graph represents one record from a data set. The distribution pattern of points from multiple records reveals, among other qualities, the correlation between the selected variables in the data set. The scatterplot is not to be confused with the correlation plot [Information Technology Lab, NIST #2] which treats already adopted correlation coefficients in different data groups, while the term correlation diagram does not seem to be bound.

Revealed Information

Type of Correlation

Perfect linear correlation results in all samples lying on the regression line with positive or negative incline dependent on the sign of the correlation coefficient [University of Illinois]. Note, that the nonzero incline of the line is insignificant in this kind of diagram [Wikipedia Correlation, EN] since it is dependent on axis scales.

Other patterns of linear correlation.

(regression function, "scatterplot smoothing" [NetMBA]) sign, strength (TODO: add about figures with: perfect positive, strong tight negative, weak loose positive, no correlation, clusters) 4 figures:

perfect positive
high negative
low positive (with regression line)
no correlation
some with regression line

Generally: refer to regression analysis for further ...

Density, Outlyers and Clusters

density (-> cluster analysis) & outlyers

1 image for clusters
1 with outlyer

Scatterplots of Higher Dimensions

Not necessarily two variables, higher dimensions displayed spacially or by point properties (color, size, shape)

TODO: add figure with colored 3D plot, sunflower plot [addictedtor.free.fr], [York University], jitter plot

Treating Discrete Data

[Wikipedia, DE]

References

Wikipedia, EN: http://en.wikipedia.org/wiki/Scatterplot
Wikipedia, DE: http://de.wikipedia.org/wiki/Streudiagramm
Wikipedia Correlation, EN: http://en.wikipedia.org/wiki/Correlation
University of Illinois: http://www.mste.uiuc.edu/courses/ci330ms/youtsey/scatterinfo.html
Information Technology Lab, NIST #1: http://www.itl.nist.gov/div898/handbook/eda/section3/eda33q.htm
Information Technology Lab, NIST #2: http://www.itl.nist.gov/div898/handbook/eda/section3/linecorr.htm
NetMBA: http://www.netmba.com/statistics/plot/scatter/
ChartItNow: http://www.chartitnow.com/scatter%20diagram.html
addictedtor.free.fr: http://addictedtor.free.fr/graphiques/graphcode.php?graph=59
York University: http://www.math.yorku.ca/SCS/sasmac/sunplot.html
NLVM: http://matti.usu.edu/nlvm/nav/frames_asid_144_g_4_t_5.html

Teaching:TUW - UE InfoVis WS 2008/09 - Gruppe 02 - Aufgabe 1 - Scatterplot

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