3.4 The SLOPE ONE Scheme The slope one schemes take into account both information from other users who
rated the same item (like the ADJUSTED COSINE ITEMBASED) and from the other items rated by the same user
(like the PER USER AVERAGE). However, the schemes also rely on data points that fall neither in the user array nor in
the item array (e.g. user A’s rating of item I in Fig. 1), but are nevertheless important information for rating prediction.
Much of the strength of the approach comes from data that is not factored in. Specifically, only those ratings by users
who have rated some common item with the predictee user and only those ratings of items that the predictee user has
also rated enter into the prediction of ratings under slope one schemes.