xts objects containing adjusted close prices of the
  S&P 500 (SP500; ticker symbol ``^GSPC''),
  Dow Jones (DJ; ticker symbol ``^DJI''),
  NASDAQ 100 (NASDAQ; ticker symbol ``^NDX''),
  FTSE 100 (FTSE; ticker symbol ``^FTSE''),
  Swiss Market Index (SMI; ticker symbol ``^SSMI''),
  Euro Stoxx 50 (EURSTOXX; ticker symbol ``^STOXX50E''),
  Cotation Assistée en Continu (CAC; ticker symbol ``^FCHI''),
  Deutscher Aktienindex (DAX; ticker sybmol ``^GDAXI''),
  China Securities Index (CSI; ticker sybmol ``000300.SS''),
  Hang Seng Index (HSI; ticker symbol ``^HSI''),
  Shanghai Stock Exchange Composite Index (SSEC; ticker symbol
  ``000001.SS'') and the
  NIKKEI (NIKKEI; ticker symbol ``^N225'')
  from their first date of availablility to 2015-12-31.