Difference between the observed and expected number of pairs where both proteins are either essential or nonessential.

The total number of pairs refers to the number of nonadjacent protein pairs with three or more common neighbors in the network. (Due to the sparsity of the Y2H network, the statistics are calculated for nonadjacent pairs having one or more neighbors in common.) The nodes in the pair are of ��the same type�� if they are both essential or both nonessential.