  Experimental and theoretical investigations on the integer quantized Hall
effect in gate defined narrow Hall bars are presented. At low electron mobility
the classical (high temperature) Hall resistance line RH(B) cuts through the
center of all Hall plateaus. In contrast, for our high mobility samples the
intersection point, at even filling factors \nu = 2; 4 ..., is clearly shifted
towards larger magnetic fields B. This asymmetry is in good agreement with
predictions of the screening theory, i. e. taking Coulomb interaction into
account. The observed effect is directly related to the formation of
incompressible strips in the Hall bar. The spin-split plateau at \nu= 1 is
found to be almost symmetric regardless of the mobility. We explain this within
the so-called effective g-model.
