  The content that a recommender system (RS) shows to users influences them.
Therefore, when choosing a recommender to deploy, one is implicitly also
choosing to induce specific internal states in users. Even more, systems
trained via long-horizon optimization will have direct incentives to manipulate
users: in this work, we focus on the incentive to shift user preferences so
they are easier to satisfy. We argue that - before deployment - system
designers should: estimate the shifts a recommender would induce; evaluate
whether such shifts would be undesirable; and perhaps even actively optimize to
avoid problematic shifts. These steps involve two challenging ingredients:
estimation requires anticipating how hypothetical algorithms would influence
user preferences if deployed - we do this by using historical user interaction
data to train a predictive user model which implicitly contains their
preference dynamics; evaluation and optimization additionally require metrics
to assess whether such influences are manipulative or otherwise unwanted - we
use the notion of "safe shifts", that define a trust region within which
behavior is safe: for instance, the natural way in which users would shift
without interference from the system could be deemed "safe". In simulated
experiments, we show that our learned preference dynamics model is effective in
estimating user preferences and how they would respond to new recommenders.
Additionally, we show that recommenders that optimize for staying in the trust
region can avoid manipulative behaviors while still generating engagement.
