  Human activities can play a crucial role in the statistical properties of
observables in many complex systems such as social, technological and economic
systems. We demonstrate this by looking into the heavy-tailed distributions of
observables in fatal plane and car accidents. Their origin is examined and can
be understood as stochastic processes that are related to human activities.
Simple mathematical models are proposed to illustrate such processes and
compared with empirical results obtained from existing databanks.
