The month of August 2011 ranks as the 10th worst month for U.S. stocks in 75 years. Or to put it another way of the last 900 months, the month of August 2011 ranks the 10th worst month in terms of volatiltiy. The average up and down movement each day in August was 1.%. In August the Dow Jones Industrial Averages were down 529 points, or a drop of 4.4%. This is not what worries investors as much- as their are months like May 2010 which had a 7.9% drop. The impact on investors is in the increased uncertainty that this creates about how an investment will perform in the future.