Although stocks seem to be in a bull market, it might be more appropriate to call this a “skinny bull” market. Incredibly, just seven companies account for 98% of the U.S. stock market’s year-to-date gains. In this article, journalist Allan Sloan details how large tech firms are responsible for driving broad indices higher. Sloan notes that rapidly rising stocks can be subject to swift reversals, a strong argument for a well-diversified portfolio.