Manouselis and Costopoulou [49] also propose three different algorithms to
compute similarities between users in multi-criteria rating settings: similarity-perpriority, similarity-per-evaluation, and similarity-per-partial-utility. The similarityper-priority algorithm computes the similarities between users based on importance
weights wc(u) of user u for each criterion c (rather than ratings R(u, i)). In this
way, it creates a neighborhood of users that have the same expressed preferences
with the target user. Then, it tries to predict the overall utility of an item for this
user, based on the total utilities of the users in the neighborhood. In addition, the
similarity-per-evaluation and similarity-per-partial-utility algorithms create separate
neighborhoods for the target user for each criterion, i.e., they calculate the similarity
with other users per individual criterion, and then predict the rating that the target
user would provide upon each individual criterion. The similarity-per-evaluation algorithm calculates the similarity based on the non-weighted ratings that the users
provide on each criterion. The similarity-per-partial-utility algorithm calculates the
similarity based on the weighted (using wc(u) of each user u) ratings that the users
provide on each criterion.