Assuming 30 trading days horizon, S&P 500 is expected to under-perform the Northern. But the index apears to be less risky and, when comparing its historical volatility, S&P 500 is 1.48 times less risky than Northern. The index trades about -0.05 of its potential returns per unit of risk. The Northern Trust Corporation is currently generating about 0.02 of returns per unit of risk over similar time horizon. If you would invest  5,796  in Northern Trust Corporation on May 20, 2013 and sell it today you would earn a total of  40.00  from holding Northern Trust Corporation or generate 0.69% return on investment over 30 days.