BWX focuses on fixed-rate local currency sovereign debt securities of investment-grade quality outside of the US with at least one-year remaining maturity. Using a sampling method in tracking the index, this means the fund will invest in a sample of securities that collectively have an investment profile similar to that of the underlying index. Developed market issuers dominate the basket due to market-value-weighting, but emerging nations are present in smaller proportions. The index is rebalanced on a monthly basis.