SP500: Returns of the Standard and Poors 500
Description
Returns of the Standard and Poors 500 Index in the 1990'sformat
A vector of returns of the Standard and Poors 500 index for all
  the trading days in 1990, 1991, ..., 1999.References
Venables, W. N. and Ripley, B. D. (2002)
  Modern Applied Statistics with S. Fourth edition.  Springer.