edge_asymmetry: Calculate an asymmetry index based on edge counts
Description
This function will calculate an asymmetry index that is a measure of whether
or not more edges are present in the left or right hemisphere of a graph for
brain MRI data. You can choose a value for each vertex, or for the whole
hemisphere.
Usage
edge_asymmetry(g, level = c("hemi", "vertex"))
Arguments
g
An igraph graph object
level
A character string indicating whether to calculate asymmetry for
each region, or the hemisphere as a whole (default: 'hemi')
Value
A data table with edge counts for both hemispheres and the asymmetry
index; if level is vertex, the data table will have
vcount(g) rows.
Details
The equation is:
$$A = \frac{E_{lh} - E_{rh}}{0.5 \times (E_{lh} + E_{rh})}$$
where lh and rh are left and right hemispheres, respectively.
The range of this measure is \([-2, 2]\) (although the limits will only be
reached if all edges are in one hemisphere), with negative numbers
indicating more edges in the right hemisphere, and a value of 0 indicating
equal number of edges in each hemisphere.