Model specification: We work in a generalized linear model framework (McCullagh and Nelder, 1989) that assumes µ ij (or some monotone function h of µ ij ) is an additive function of (1) the rater bias α i of user i since some users may have a tendency of rating comments more positively or negatively than others, (2) popularity β j of comment j, which could reflect the quality of the comment in this setting, and (3) the author reputation γ a(j) of user a(j) since comments by a reputed author may in general get more positive ratings.
the overall bias is In addition to the bias, we include terms that capture interactions among entities (raters, authors, comments).