brainGraph (version 0.48.0)

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"), .parallel = TRUE)

Arguments

g

The igraph graph object

level

A character string indicating whether to calculate asymmetry for each region, or the hemisphere as a whole (default: 'hemi')

.parallel

Logical indicating whether or not to use foreach (default: TRUE)

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.