The different behavior of the re-ranking model in the LUNA and MEDIA corpora is due partially to the task complexity, but it is mainly due to the fact that CRFs have been deeply studied and experimented (see (Hahn et al., 2008)) on MEDIA.
table 4 shows the results of the SLU experiments on the MEDIA and LUNA test sets using the manual transcriptions of spoken sentences and a re-ranker based on PtK and the FEAtURES structure (already reported in the previous table).