The connectivity metric between a pair of genes i and j, or kij, is a transformed correlation between their expression profiles, with the matrix A = (kij) known as the unsigned adjacency matrix. kij is defined as |rij|β, using the absolute value of rij, the Pearson correlation coefficient between the profiles of genes i and j, and β is the parameter of a power function. β is selected using the fitting index proposed by Zhang et al. 117, i.e., to maximize the scale-free topology model fitting index r2 of the linear model that regresses log(p(k)) on log(k), where k is connectivity and p(k) is the frequency distribution of connectivity. For the current data, we used an R2 cutoff of 0.8, which corresponded to a selection of β = 6.5 and β = 9 for the control and schizophrenia networks, respectively.
