Mid-cap stocks have often been overlooked in favor of other size ranges in investment practice and in academic literature. Yet mid-caps have outperformed large- and small-caps, historically: the S&P MidCap 400 has beaten the S&P 500® and the S&P SmallCap 600® by an annualized rate of 2.03% and 0.92%, respectively, since December 1994. To better understand the historical outperformance by mid-caps, as well as their potential use within an investment portfolio, this paper:
- Provides an overview of S&P Dow Jones Indices’ methodology for defining the U.S. mid-cap equity universe;
- Outlines the so-called “mid-cap premium,” analyzing it from factor and sector perspectives;
- Shows that active managers have underperformed the S&P MidCap 400, historically;
- Highlights how mid-caps can be incorporated within a portfolio.
U.S. equity indices have a long history of measuring the performance of market segments. The Dow Jones Transportation Average™, the first index and a precursor to the Dow Jones Industrial Average®, was created in 1884. The inaugural capitalization-weighted U.S. equity index was first published in 1923 and evolved into today’s widely followed 500-company U.S. equity benchmark—the S&P 500.
More recently, after academic literature demonstrated the existence of a size factor, index providers developed benchmarks to track the performance of smaller companies. Among them were the S&P MidCap 400 and the S&P SmallCap 600, launched in June 1991 and October 1994, respectively.
Despite the historical outperformance of mid-cap stocks, they appear to be under-allocated compared to small-caps. Exhibit 2 shows the proportion of assets invested in core U.S. equities, across the large-, mid-, and small-cap size ranges, by U.S.-domiciled retail and institutional funds at the end of 2018. Based on overall market capitalization, we might expect funds to allocate twice as much to mid-caps compared to smallcaps. Instead, the aggregate core allocation to small- and mid-caps is approximately the same: investors appear to have a preference for smallcaps over mid-caps in their core holdings. The data shows this preference is especially true for active funds.