Conventional parameter estimates are affected (in some way or other) by the likelihood function for a parameter, and the likelihood function is such that longer documents exert a greater influence on the overall likelihood for a parameter.
we note that if the true binomial parameter θ ij for the j-th word in the i-th document were known, then the most sensible expected value for the distribution over θ j would be: Whereas the expected value of conventional method-of-moments estimate is: a weighted mean of the maximum likelihood estimates of each of the θ ij , with weights given by p (θ ij ), i.e.