If you will accept a little oversimplification, the last decade or so of global equity market performance can be summarized as follows. US stocks have profoundly outperformed stocks in the rest of the world, whether other developed markets or emerging markets. This outperformance has been partially driven by US P/E ratios expanding more than in other markets. But the largest driver of the outperformance has been the massive superiority of earnings growth in the US relative to anywhere else. This superior earnings growth has been driven not so much by strong top-line growth, but by expanding profitability by US companies relative to sales, gross profits, or other measures that can plausibly be used as proxies for economic capital. Unlike in past cycles, this rising profitability seems to have been neither a result of, nor a driver of, increased corporate investment. Digging a little deeper, we can see that the improvement in profitability has occurred only in the largest companies. These companies have been out-earning their smaller brethren by increasing margins over the past 25 years or so. The long period of their improvement suggests this effect is not something we should expect to correct over a single business cycle, but my guess is that the world in the future will be less favorable to these large, dominant companies than is true of the current environment.

