تعیین کمیت نوسانات در سیستم های اقتصادی با روش تطبیق فیزیک آماری

The emerging subfield of econophysics explores the degree to which certain concepts and methods from statistical physics can be appropriately modified and adapted to provide new insights into questions that have been the focus of interest in the economics community. Here we give a brief overview of two examples of research topics that are receiving recent attention. A first topic is the characterization of the dynamics of stock price fluctuations. For example, we investigate the relation between trading activity – measured by the number of transactions NΔt – and the price change GΔt for a given stock, over a time interval View the MathML source. We relate the time-dependent standard deviation of price fluctuations – volatility – to two microscopic quantities: the number of transactions NΔt in Δt and the variance WΔt2 of the price changes for all transactions in Δt. Our work indicates that while the pronounced tails in the distribution of price fluctuations arise from WΔt, the long-range correlations found in ∣GΔt∣ are largely due to NΔt. We also investigate the relation between price fluctuations and the number of shares QΔt traded in Δt. We find that the distribution of QΔt is consistent with a stable Lévy distribution, suggesting a Lévy scaling relationship between QΔt and NΔt, which would provide one explanation for volume-volatility co-movement. A second topic concerns cross-correlations between the price fluctuations of different stocks. We adapt a conceptual framework, random matrix theory (RMT), first used in physics to interpret statistical properties of nuclear energy spectra. RMT makes predictions for the statistical properties of matrices that are universal, that is, do not depend on the interactions between the elements comprising the system. In physics systems, deviations from the predictions of RMT provide clues regarding the mechanisms controlling the dynamics of a given system, so this framework can be of potential value if applied to economic systems. We discuss a systematic comparison between the statistics of the cross-correlation matrix View the MathML source – whose elements Cij are the correlation-coefficients between the returns of stock i and j – and that of a random matrix having the same symmetry properties. Our work suggests that RMT can be used to distinguish random and non-random parts of View the MathML source; the non-random part of View the MathML source, which deviates from RMT results provides information regarding genuine cross-correlations between stocks.