Results for an investment in stocks are based on annual rates of return for the S&P 500 index. Results for an investment in gold are based on IBA year-end prices. Results for bonds are based on annual rates of return for 10-year Treasury notes. Results for an investment in savings are based on average yields for 6-month certificates of deposit, which we've substituted for a basic savings account. Historical data on savings account interest rates is not available. Many thanks to Tenpao Lee Ph.D., professor of economics at Niagara University, for the underlying data.