Intersections I

Intersections between two or more variables

Venn and Euler Diagrams

Venn diagrams are a popular choice for showing absolute counts of the same variable tested in different conditions. An example would be over-expressed genes identified in a systematic screen of several different comparisons. The question being asked is to what extent is the composition of the variable (i.e. over-expressed genes) consistent under different conditions. The key to a useful Venn diagram is to show all possible pairwise comparisons and allow the size of the circles and overlap to be proportional to their actual values.

Euler diagrams are an extension of Venn diagrams, with a relaxation on the criteria that all possible combinations must be depicted. This means that there can potentially be several groups which are included in the diagram but do not overlap with any other groups. A common use of Euler diagrams is to show progressive sub-setting of a data set. For example, it is common to use several criteria on the out-put of a systematic screen to whittle down a list of many genes to a manageable number of interesting identifications. A visualisation of this process is depicted in figure @ref(fig:Venn-and-Euler).

But this is better…

Better venneuler version