  We reconsider the theory of Hall effect in the systems with hopping
conduction. The purpose of the present study is to compare the percolation
approach based on the optimal triad model with numerical simulations and recent
experimental results. We show that, in the nearest neighbor hopping regime, the
results of the percolation theory agree to the simulation. However, in the
variable range hopping (VRH) regime, the optimal triad model fails to describe
the numerical results. It is related to the extremely small probability to find
the optimal triad of sites in the percolation cluster in the VRH regime. The
contribution of these triads to the Hall effect appears to be small. We
describe the Hall mobility in the VRH regime with the empirical law obtained
from the numerical results. The law is in agreement with our recent
experimental data in 2D quantum dot arrays with the hopping transport.
