Original sentence: Media Matters for America, a liberal group, has stated that MSNBC carries a conservative bias, meanwhile a conservative media watchdog group, Media Research Center, has argued that MSNBC has a liberal slant
Edited sentence: Media Matters for America, a liberal group, has stated that MSNBC carries a conservative bias, meanwhile a conservative media watchdog group, Media Research Center, has correctly argued that MSNBC has a liberal slant