In terms of granularity, this task has been investigated from building word level sentiment lexicon (Turney, 2002;Moilanen and Pulman, 2008) to detecting phrase-level (Wilson et al., 2005;Agarwal et al., 2009) and sentence-level (Riloff and Wiebe, 2003;Hu and Liu, 2004) sentiment orientation.
adding the polarized bigram feature and transition feature (PB and T) individually can yield some improvement; however, adding both of them did not result in any further improvement -performance degrades compared to LF+PB.