MDY tracks the S&P MidCap 400, the same index as IJH, and was the first mid-cap ETF, launched in 1995. It is a unit investment trust, so it cannot reinvest dividends immediately, and its expense ratio is higher than that of IJH or VO. The index holds about 400 US mid-sized companies that meet profitability and liquidity requirements. For long-term holders the same exposure is available at lower cost in other funds, while MDY remains an established, liquid option for traders.
