edge_asymmetry {brainGraph}

Calculate an asymmetry index based on edge counts

Description

Calculate an asymmetry index, a ratio of intra-hemispheric edges in the left to right hemisphere of a graph for brain MRI data.

Usage

edge_asymmetry(g, level = c("hemi", "vertex"), A = NULL)

Arguments

g

An igraph graph object

level

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

A

Numeric matrix; the adjacency matrix of the input graph. Default: NULL

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.

The level argument specifies whether to calculate asymmetry for each vertex, or for the whole hemisphere.

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.

Author(s)

Christopher G. Watson, [e-mail]