In a nondegenerate three-level ladder-type atomic system, the transmission spectrum of a probe field through the rubidium atomic vapor, theoretically and experimentally, was investigated by tuning the probe field intensity. An expression for the probe response was derived analytically by using the dressed perturbation method, which predicted the existence of electromagnetically induced absorption (EIA) when the probe field was no longer weak enough. Experimentally, in the D2 line of rubidium atom in a room temperature vapor cell, when switching from weak probe field to strong probe field, it was not limited to the single photon resonance condition, and the conversion of electromagnetically induced transparency (EIT) into EIA at different probe detuning was realized. The main reason for the formation of EIA was the constructive interference between secondary dressed states generated by strong probe field and coupling field, which was analyzed by using the dressed-state image. Since many applications of EIT and EIA relied on an anomalous dispersion near the resonance, a new ability to control the sign of the dispersion was introduced.