The effects of the neutron-proton interaction on the low-lying levels of Mo and Cd isotopes have been considered in the frame of the IBA-1 model by taking into account an effective boson number (N eff). Both an empirical procedure based on previous IBA-2 mixing calculations and theN p N n scheme provide comparableN eff values. Level spectra and electromagnetic transitions are investigated. The results support the idea that IBA-1 calculations with a suitableN eff can largely simulate IBA-2 mixing calculations, taking advantage of simplicity and a smaller number of parameters.