The parameters of T back are estimated as follows: where α(t) is a discounting coefficient and β is set to satisfy that all words P (w|t) = 1.
the discounting coefficient is computed using the Witten-Bell discounting method: where C anno (t) is the count of tokens whose tag is t in the manually annotated corpus and S anno (t) is the seen types of words with tag t. we trust the parameter estimates from the model trained on manual annotation by default unless it is based on unreliable statistics.