The Vanguard Value ETF (Ticker: VTV) seeks investment results that correspond generally to the performance, before fees and expenses, of the MSCI US Prime Market Value Index. The index represents the large cap value companies in the MSCI US Prime Market 750 Index. MSCI uses 3 key factors to determine value on a semi-annual basis. Those factors are the book value to price ratio, 12-month forward earnings to price ratio and dividend yield. Buffer zones help limit index turnover caused by temporary migration of securities from one size index to another during quarterly size reviews and from one style to the other during semi-annual style reviews.