  The origin of non-Poissonian or bursty temporal patterns observed in various
datasets for human social dynamics has been extensively studied, yet its
understanding still remains incomplete. Considering the fact that humans are
social beings, a fundamental question arises: Is the bursty human dynamics
dominated by individual characteristics or by interaction between individuals?
In this paper we address this question by analyzing the Wikipedia edit history
to see how spontaneous individual editors are in initiating bursty periods of
editing, i.e., individual-driven burstiness, and to what extent such editors'
behaviors are driven by interaction with other editors in those periods, i.e.,
interaction-driven burstiness. We quantify the degree of initiative (DoI) of an
editor of interest in each Wikipedia article by using the statistics of bursty
periods containing the editor's edits. The integrated value of the DoI over all
relevant timescales reveals which is dominant between individual-driven and
interaction-driven burstiness. We empirically find that this value tends to be
larger for weaker temporal correlations in the editor's editing behavior and/or
stronger editorial correlations. These empirical findings are successfully
confirmed by deriving an analytic form of the DoI from a model capturing the
essential features of the edit sequence. Thus our approach provides a deeper
insight into the origin and underlying mechanisms of bursts in human social
dynamics.
