Adapting Recommendation Diversity to Openness to Experience: A Study of Human Behaviour Nava Tintarev, Matt Dennis, and Judith Masthoff Department of Computing Science ⋆ University of Aberdeen {n.tintarev,m.dennis,j.masthoff}@abdn.ac.uk Abstract. This paper uses a User-as-Wizard approach to evaluate how people apply diversity to a set of recommendations. In particular, it con- siders how diversity is applied for a recipient with high or low Openness to Experience, a personality trait from the Five Factor Model. While there was no effect of the personality trait on the degree of diversity applied, there seems to be a trend in the way in which it was applied. Maxi- mal categorical diversity (across genres) was more likely to be applied to those with high Openness to Experience, at the expense of maximal thematic diversity (within genres). Keywords: Diversity, Serendipity, Personality, Recommender Systems 1 Introduction Recommender systems offer items for a user to try or buy based on what is known about their previous preferences or behaviours. Often these recommendations are presented as a list of items. Historically, the emphasis has been on ensuring that items are useful to the user. More recently, the need for diverse recommendations has been recognized by the recommender systems community [1–4]. There is some consensus that personality is a key aspect to consider when injecting novelty and diversity into recommendations, since attitudes towards new or diverse experiences vary considerably amongst users [5]. Such a recom- mender system would therefore require a model which accurately describes the personality of users. The trait model from Psychology is a fitting candidate for this. It describes a user’s personality by scores on several dimensions, called traits, which are measured via validated self-report questionnaires. Among trait models, the Five Factor Model [6] (FFM, also known as the Big 5 model) has been shown to have excellent reliability in practice [7]. The model describes the personality of an individual by five traits: Extraversion (I), Agreeableness (II), Conscientiousness (III), Emotional Stability (IV), and Openness to Experience ⋆ This research has been funded by the Engineering and Physical Sciences Research Council (EPSRC, UK), grant ref. EP/J012084/1