positive backoff weight

[Solen Quiniou]

Thank you for the past answers to my questions.

I've got another question. Sometimes, when I use a Good-Turing 
discounting, some of the backoff weight of the unigram (I compute a 
bigram model) are positive log-probability. How is it possible ? Is it 
because Good-Turing discounting is disabled on unigram since there are 
no unigram which frequency is 1 ? And, more, generally, how are computed 
backoff weights for unigrams, in the case of a bigram model ?

Thanks a lot for your answers.
Solen.