23.5.1 Output Uncertainty
In Output Uncertainty-based methods, an item to label (training point) is selected
so as to reduce the uncertainty of rating predictions for test items. In Figure 23.1,
with the assumption that the RS estimates the rating of an item based on the cluster
to which it belongs (e.g. items in the same movie genre receive the same rating),
if a user’s rating for a movie from the Sci-Fi genre (upper-right) has already been
obtained, then there is a higher likelihood that the RS may be more certain about
the ratings of other movies in the Sci-Fi genre, likely making it more beneficial to
obtain a user’s preference for a movie from a genre (cluster) not yet sampled, i.e. a
cluster that is still uncertain.