  Personalization, including both self-selected and pre-selected, is inevitable
when tremendous amounts of media content are available. Personalization, which
is believed to cause people to consume fewer diverse contents, can lead to
fragmentation and polarization in society. Therefore, it is important to
investigate the diversity of consumed contents over time. In this paper, first,
we propose a framework to measure and analyze how the diversity of the consumed
contents of users changes over time. In our framework, we introduce a new
metric to measure content diversity based on our redefinition of diversity.
Then, we investigate the relationship between selective exposure and content
diversity changes using our framework and examine what factors encourage people
to consume contents that are more diverse. We find that people autonomously
consume more diverse contents from a macro-perspective without an external
influence, suggesting that people are less likely to be fragmented and
polarized, although from a micro-perspective they consume limited contents. We
also obtain evidence that users who consume highly ambiguous contents tend to
increase the diversity of their consumed contents.
