squad changes. There are, of course, other external factors
which eVect the outcome of a game. So, even in the best
case we expect to have noise in the data. Since players,
except Wilson, are only considered from the point of view
of playing or not playing, the eVect of any player who was
always present will be ignored. This is because the learners
can only compare the diVerence in the outcome of matches
with a player present or absent.
It is also worth noting that all the models (including the
expert BN) are inherently asymmetric. Whereas for Spurs
we consider the particular players involved in any given
match to be signiWcant, for all their opponents we only have
a general rating for their overall quality.