Providing computer-based systems and methods for analyzing historical performance of financial securities and identifying trades in those securities based on the securities' current position as compared to this historical performance. These computer-based systems and computer-implemented methods include identifying stock pairs to include in a trading portfolio, based on a measure of the pair's relative performance, such as a modified Sharpe Ratio. The value of the stocks in each stock pair in the portfolio is assessed and deviations determined. This assessment can occur daily or at a longer or shorter time step. Stocks are bought or sold based on the current price of the stock as compared to historical performance. The present invention preferably employs a large number of stock pairs in the trading portfolio. This use of a large number of pairs results in a plurality of stocks being in more than one stock pair.