The investment seeks to track the investment results (before fees and expenses) of the Zacks Mid-Cap Core Index (the underlying index). The fund generally will invest at least 90% of its total assets in the securities that comprise the underlying index, as well as American depositary receipts (ADRs) that represent securities in the underlying index. The underlying index is composed of 100 securities that Zacks selects from a universe of mid-capitalization securities including common stocks, master limited partnerships (MLPs), ADRs, real estate investment trusts (REITs) and business development companies (BDCs).