This letter investigates the impact of reference frames in Distributed Video Coding (DVC) on the Rate-Distortion (RD) performance and reveals that reference frames have the potential to be better side information (SI) than the extensively used interpolated frames. Based on this investigation, we also propose a motion range prediction (MRP) method to exploit reference frames and precisely guide the statistical motion learning process. Extensive simulation results show that choosing reference frames as SI performs competitively, and sometimes even better than interpolated frames. Furthermore, the proposed MRP method is shown to significantly reduce the decoding complexity without degrading any RD performance.