The problem that arises 
here is that since many disfluent words are copies 
of fluent words, if the same cost is used to align 
fluent and disfluent words, the alignment will be 
ambiguous (i.e. there will be multiple alignments with the same cost).
as shown in Table 1, the alignment cost is slightly higher for inserting, copying and substituting a disfluent word and slightly lower for deleting a disfluent word.