  Multi-objective recommender systems (MORS) provide suggestions to users
according to multiple (and possibly conflicting) goals. When a system optimizes
its results at the individual-user level, it tailors them on a user's
propensity towards the different objectives. Hence, the capability to
understand users' fine-grained needs towards each goal is crucial. In this
paper, we present the results of a user study in which we monitored the way
users interacted with recommended items, as well as their self-proclaimed
propensities towards relevance, novelty and diversity objectives. The study was
divided into several sessions, where users evaluated recommendation lists
originating from a relevance-only single-objective baseline as well as MORS. We
show that despite MORS-based recommendations attracted less selections, its
presence in the early sessions is crucial for users' satisfaction in the later
stages. Surprisingly, the self-proclaimed willingness of users to interact with
novel and diverse items is not always reflected in the recommendations they
accept. Post-study questionnaires provide insights on how to deal with this
matter, suggesting that MORS-based results should be accompanied by elements
that allow users to understand the recommendations, so as to facilitate their
acceptance.
