About 60 percent of the 222 sample points in Table 1 concerned stock markets. Thus, the evidence supporting the resilience pattern for stock markets was particularly strong. Yet, it was important also to show that the resilience effect is not confined to stock markets for it suggests that a possible theoretical framework should apply to other speculative markets as well.

Let us now briefly discuss the significance and possible implications of the present finding. In the late 1990s econophysicists along with some economists ([3]) devoted great attention to the statistical analysis of stock market indexes, the overall objective being the identification of possible scaling laws. Yet, indexes do not give great insight into the internal mechanisms of stock markets. Such an understanding can only be gained by opening the “black box” and studying the interactions that take place between individual stocks.

This idea has recently gained more acceptance as shown by a number of innovative papers going into that direction; e.g. [3, 4, 6 ]. Finally, let us briefly consider the next step, namely the construction of a theoretical framework. Obviously any model is (and has to be) a schematization of the real world; therefore, constructing a “realistic” model cannot be a viable and suitable objective; models need more precise “targets” and “guiding lights”.

In a number of recent empirical studies we have tried to define such targets: the sharp peak - flat trough pattern [9, 10], the price multiplier effect [7, 9], the relationship between stock market crashes and increases in interest rate spread [8] define quantitative patterns which provide useful guiding lights for the construction of a theoretical framework. On the theoretical side some promising advances have been made recently which can possible provide an adequate framework for the description of the internal machinery of stock markets. For instance one would not be surprised to see percolation (see in this respect [2]) play a role in the spread of a bubble; after all, a speculative outburst can be seen as propagating from high-growth stocks to low-growth stocks in the same way as a technical innovation progressively gains acceptance in an economy.

Acknowledgments I would like to express my gratitude to the statistical experts of the Halifax Company (U.K.) and the Chambre des Notaires (Paris) for their kind assistance.

By Dr B.M. Roehner

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