Physica A 387 (2008) 6391–6394
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Physica A
journal homepage: www.elsevier.com/locate/physa
Empirical analysis on temporal statistics of human
correspondence patterns
Nan-Nan Li
a
, Ning Zhang
a
, Tao Zhou
b,c,∗
a
Business School, University of Shanghai for Science and Technology, Shanghai 200093, PR China
b
Department of Modern Physics, University of Science and Technology of China, Hefei 230026, PR China
c
Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
a r t i c l e i n f o
Article history:
Received 20 April 2008
Received in revised form 17 July 2008
Available online 25 July 2008
Keywords:
Human dynamics
Correspondence patterns
Burstiness
Power-law distribution
a b s t r a c t
Recently, extensive empirical evidence shows that the timing of human behaviors obeys
non-Possion statistics with heavy-tailed interevent time distribution. In this paper, we
empirically study the correspondence pattern of a great Chinese scientist, named Hsue-Shen
Tsien. Both the interevent time distribution and response time distributions deviate from
the Poisson statistics, showing an approximate power-law decaying. The two power-law
exponents are more or less the same (about 2.1), which strongly support the hypothesis in
[A. Vázquez, J.G. Oliveira, Z. Dezsö, K.-I. Goh, I. Kondor, A.-L. Barabási, Phys. Rev. E 73 (2006)
036127] that the response time distribution of the tasks could in fact drive the interevent
time distribution, and both the two distributions should decay with the same exponent.
Our result is against the claim in [A. Vázquez, J.G. Oliveira, Z. Dezsö, K.-I. Goh, I. Kondor,
A.-L. Barabási, Phys. Rev. E 73 (2006) 036127], which suggests the human correspondence
pattern belongs to a universality class with exponent 1.5.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
Being a joint interest of sociology, psychology and economics, human behaviors have been extensively investigated
during the last few decades. However, up to now, most of the academic reports on human behaviors are based on clinical
records and laboratorial data, and most of the corresponding hypotheses and conclusions are only qualitative. Therefore,
the establishment of a quantitative theory on human behaviors becomes one of the main scientific interests nowadays [1,2].
Traditionally, the individual activity pattern is generally simplified as a Poisson process, leading to an exponential interevent
time distribution [3]. In such conditions, the probability density function of the recorded time intervals, τ , between two
consecutive events has an exponential form as p
(
τ
)
= λe
−λτ
.
However, with the prompt development of computer technology recently, more and more empirical studies show
that many human activities deviate from the Poisson process [4,5]: our activity patterns follow non-Poisson statistics,
characterized by bursts of rapidly occurring events separated by long periods of inactivity. Those heavy-tailed distributions,
well approximated by a power-law p(τ ) ∼ τ
−γ
, are observed in many real systems, including e-mail communication [4],
commercial transactions [6], web browsing [7,8], movies-on-demand [9], online games [10], human correspondence
patterns [11], short-messages communication [12], computer operations [13], and so on. The discovery of this phenomenon
has opened a new research direction namely human dynamics. So far, the underlying mechanism leading to those non-
Poisson statistics is not clear. Barabási and his colleagues [4,6] have recently proposed that the bursty nature of human
dynamics is a consequence of a queuing process driven by human decision making: whenever an individual is presented
∗
Corresponding author at: Department of Modern Physics, University of Science and Technology of China, Hefei 230026, PR China.
E-mail address: zhutou@ustc.edu (T. Zhou).
0378-4371/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.physa.2008.07.021