In this paper, we investigate the impact of interference on the performance of selection based parallel multiuser scheduling. In conventional parallel multiuser scheduling schemes, every scheduled user is interfering with every other scheduled user. This is a factor which limits the capacity and performance of multiuser systems and the level of interference becomes substantial as the number of scheduled users increases. Based on the above motivation, we investigate the trade-off between the throughput and the number of scheduled users. The major difficulty in the total average sum rate capacity and the average spectral efficiency (ASE) analysis resides in the determination of the statistics of the Signal to Interference plus Noise Ration (SINR) of the scheduled user. Fortunately, we could derive the accurate statistical characterization of the SINR of the scheduled user. With these accurate statistical analysis, we derive the total average sum rate capacity and the average spectral efficiency based on the SINR. Based on the ASE and the total average sum rate capacity analysis, we investigate the trade-off between the throughput and the number of scheduled users. Hence, based on these results, the system should carefully select the appropriate number of scheduled users to maximize the overall throughput while maintaining an acceptable quality of service given certain channel conditions.