source: orange/docs/widgets/rst/visualize/sievediagram.rst @ 11050:e3c4699ca155

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1.. _Sieve Diagram:
2
3Sieve Diagram
4=============
5
6.. image:: ../icons/SieveDiagram.png
7
8Plots a sieve diagram for a pair of attributes.
9
10Signals
11-------
12
13Inputs:
14   - Examples (ExampleTable)
15      Input data set.
16
17
18Outputs:
19   - None
20
21
22Description
23-----------
24
25A sieve diagram is a graphical method for
26visualizing the frequencies in a two-way contingency table
27and comparing them
28to the expected frequencies under assumtion of independence. The sieve diagram was proposed by Riedwyl and Schüpbach in a technical report in 1983 and later called a parquet diagram <a href="#Riedwyl and Schüpbach" title="">(Riedwyl and Schüpbach, 1994)</a>. In this display the area of each rectangle is proportional to expected frequency and observed frequency is shown by the number of squares in each rectangle. The difference between observed and expected frequency (proportional to standard Pearson residual) appears as the density of shading, using color to indicate whether the deviation from independence is positive (blue) or negative (red).
29
30The snapshot below shows a sieve diagram for Titanic data set and attributes sex and survived (the later is actually a class attribute in this data set). The plot shows that the two variables are highly associated, as there are substantial differences between observed and expected frequencies in all of the four quadrants. For example and as highlighted in a balloon, the chance for not surviving the accident was for female passengers much lower than expected (0.05 vs. 0.14).
31
32.. image:: images/SieveDiagram-Titanic.png
33
34Orange can help to identify pairs of attributes with interesting associations. Such attribute pairs are upon request (:obj:`Calculate Chi Squares`) listed in :obj:`Interesting attribute pair`. As it turns out, the most interesting attribute pair in Titanic data set is indeed the one we show in the above snapshot. For a contrast, the sieve diagram of the least interesting pair (age vs. survival) is shown below.
35
36.. image:: images/SieveDiagram-Titanic-age-survived.png
37
38References
39----------
40
41  - Riedwyl, H., and Schüpbach, M. (1994). Parquet diagram to plot contingency tables. In  Softstat '93: Advances in Statistical Software, F. Faulbaum (Ed.). New York: Gustav Fischer, 293-299.
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