The effective collision frequency v(eff) of electrons in capacitively driven discharges of Ar/Kr, Cl-2 and BCl3 has been investigated using self-excited electron resonance spectroscopy. The most prominent features are the steep increase of v(eff) at low power inputs in all three gases and a slight but systematic decrease of v(eff) versus p for Ar/Kr and BCl3 over the whole pressure range investigated. At medium pressures, the effective collision rate v(eff) in Cl-2 increases by 2 orders of magnitude which is a clear manifestation for the transition from stochastic to ohmic heating. These features have been correlated with data gained with a V(I) probe. The dependence of the ohmic discharge resistance is mainly determined by the drastic change of v(eff) rather than by the variation of electron density n(e). (c) 2005 American Vacuum Society.