this way the high intricacy of several co-and counter-acting processes is considered. It reflects that big data reveal correlations and dependencies that cannot be seen when studying small data sets, and, in difference to the past, it is accepted that a detailed causal explanation is not always possible. Causal inference, when possible, may not necessarily be expressed in terms of a simple, closed analytic equation or an insightful, simple physical model. We will get back to this point below.