Scatter fan map

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A scattering card compartments (English: fan chart ) consists of a group of spread compartments, which can be positioned by two categorization dimensions. A dispersion fan is a circular diagram that shows the same information about dispersion as a box plot , namely median , quartile and two extreme values.

construction

Legend for the scatter fan and comparison with box plot

A dispersion fan consists of:

  1. a circular line as a scale,
  2. a diameter line to display the median,
  3. the fan (a segment of a circle) to display the quartiles
  4. two springs to display the extreme values.

The scale begins on the circular line on the far left with the start value (for example with zero). The other values ​​are plotted clockwise. The white end of the diameter line shows the value of the median. The dark fan shows the spread of the middle 50% of the measured values; so it ranges from the first to the third quartile. The white feathers show the spread of the middle 90% of the measured values.

The length of the white section of the diameter line corresponds to the number of measured values.

application

A fan-spread map provides a quick overview of the characteristics of a measured value that is dependent on two variables. This is possible thanks to the compact display and the fixed expansion of the individual scatter fans, independent of the values ​​shown.

The main advantage of a fan map compared to a group of box plots is that the fans can be compared not only in one direction, but in two directions (horizontal and vertical).

example

The MathAchieve data set used for the following example comes from the nlme R package by Jose Pinheiro et al. It contains results for math exams from 7185 students. The students are categorized according to gender and belonging to an ethnic minority.

7185 math exams: results according to gender and belonging to a minority

The graph shows the test results as a function of the socio-economic status of the students (x-axis) and the average socio-economic status of fellow students at their school (y-axis). In the four main graphic fields, students are distinguished according to their gender and according to whether they belong to a minority.

This graphic clearly shows how the mean value partly follows a major main trend, although the values ​​in the individual subgroups (in the cells) vary widely and one could therefore be in doubt about a possible correlation.

See also

Individual evidence

  1. ^ [1] Fischer, Wolfram (2010): New graphics for data visualization. Volume 1. Spoke graphics, fan charts, difference, sequence and alternating diagrams. Wolfertswil (ZIM). ISBN 978-3-905764-06-2 .
  2. ^ [2] Fischer, Wolfram (2010): Scattering fan map to visualize a twofold dependency. Wolfertswil (ZIM).
  3. ↑ Jose Pinheiro et al: nlme: Linear and Nonlinear Mixed Effects Models ( English ) cran.r-project.org. July 11, 2019. Retrieved November 10, 2019.

literature