  Polarization of opinion is an important feature of public debate on
political, social and cultural topics. The availability of large internet
databases of users' ratings has permitted quantitative analysis of polarization
trends-for instance, previous studies have included analyses of controversial
topics on Wikipedia, as well as the relationship between online reviews and a
product's perceived quality. Here, we study the dynamics of polarization in the
movie ratings collected by the Internet Movie database (IMDb) website in
relation to films produced over the period 1915-2015. We define two statistical
indexes, dubbed hard and soft controversiality, which quantify polarized and
uniform rating distributions, respectively. We find that controversy decreases
with popularity and that hard controversy is relatively rare. Our findings also
suggest that more recent movies are more controversial than older ones and we
detect a trend of "convergence to the mainstream" with a time scale of roughly
40-50 years. This phenomenon appears qualitatively different from trends
observed in both online reviews of commercial products and in political debate,
and we speculate that it may be connected with the absence of long-lived "echo
chambers" in the cultural domain. This hypothesis can and should be tested by
extending our analysis to other forms of cultural expression and/or to
databases with different demographic user bases.
