NYSE Composite Index - 2007

The following graph plots the year-to-date performance of the index for 2007 compared to the probability calculated by a random walk model.

Initial Value: 9139.02 Hist. Volatility: 0.57% Annual Drift: 7% Final Value: 9740.32 Percentile: 50%
Click on the image for the high resolution version.

The high to date and low to date prices of the stock plotted against a random walk model for 2007 (what's this?).