Our new score, F P P (W ), which is a combination of PP and TF, is defined as their product: F P P (W ) = tf (W )P P (W ) ⇒ log 2 F P P (W ) = log 2 tf (W ) + log 2 P P (W ) We avoided the problem of log 2 tf (W ) being undefined with tf (W ) = 0 5 by applying the adding-one smoothing to tf (W ).
the above definition of log F P P (W ) changed as follows: We used this log 2 F P P (W ) measure for evaluation.