According to a recent article in the Wall Street Journal, the golden rule of investing---reduce risk by diversifying your money---is getting harder to follow. Research shows that a number of investments whose prices once rose and fell independently of each other are now increasingly correlated. The Journal quotes a recent report from Merrill Lynch & Co, which found that small stocks were 94% correlated to the broad Standard & Poorâ€™s 500-stock Index. Simply put, when the S&P 500 rose, an index of small stocks also rose 94% of the time---only 6 years ago, the figure was at 62%. Even commodities like oil and precious metals are increasingly moving together with stocks. As a physician-investor, you must now work harder to diversify your portfolio so that all of your investments donâ€™t potentially crash at the same time. Experts quoted in the Journal recommend investing in uncorrelated assets, such as bonds and cash---and also funds that invest in high-quality bonds like long-term government bonds or corporate bonds with high credit ratings. Unfortunately, these investment vehicles have had small returns over the past 2 years.