In Table 2 
is varied for BM11 with the other
parameters held at zero. As the value of 
increases from zero to
about 2 performance improves sharply, then deteriorates gradually. Even
very small values of 
have a marked effect, because the wide
variation in document length implies that the term 
in equation 10 can be quite large even when
is as low as 0.05.
: Effect of varying the document term frequency parameter 
