Fig 5. Cluster analysis of methods.

Each dot corresponds to a reviewed paper; the brown bubbles correspond to the keywords describing the techniques. A connection between a paper and a keyword occurs when the related technique is used. The size of the bubble increases (logarithmically) with the number of papers citing the keyword. For visual purpose only, i) the bubbles are displayed with different shades of brown and ii) the technical keywords (listed in S1 Table in the Supporting Information) describing methods used by only one paper are not displayed (the full set is shown in S1 Fig in the Supporting Information). The graph was produced by using the i-graph package[13] in R.