  Although recent studies have found that the long-term correlations relating
to the fat-tailed distribution of inter-event times exist in human activity,
and that these correlations indicate the presence of fractality, the property
of fractality and its origin have not been analyzed. We use both DFA and MFDFA
to analyze the time series in online viewing activity separating from Movielens
and Netflix. We find long-term correlations at both the individual and communal
level, and that the extent of correlation at the individual level is determined
by the activity level. These long-term correlations also indicate that there is
fractality in the pattern of online viewing. And, we firstly find a
multifractality that results from the combined effect of the fat-tailed
distribution of inter-event times (i.e., the times between successive viewing
actions of individual) and the long-term correlations in online viewing
activity and verify this finding using three synthesized series. Therefore, it
can be concluded that the multifractality in online viewing activity is caused
by both the fat-tailed distribution of inter-event times and the long-term
correlations, and that this enlarges the generic property of human activity to
include not just physical space, but also cyberspace.
