Comparison between volatility return intervals of the S&P 500 index and two common models I. Vodenska-Chitkushev, F. Z. Wang, P. Weber, K. Yamasaki, S. Havlin and H. E. Stanley Eur. Phys. J. B, 61 2 (2008) 217-223 Published online: 16 February 2008 DOI: 10.1140/epjb/e2008-00066-4