Stratified sampling allows us to select a subset of bonds that have similar
characteristics of a bond index, without having to hold every single bond.
As a result, key
characteristics of a bond index, such as the average maturity of bonds in the index, can change every year.
Not exact matches
Bonds of an
index with similar
characteristics can be grouped together and will have similar risk attributes.
Indices that use independent data sources and global
indexing standards also help raise the level
of information about the
characteristics of opaque
bond markets.
These funds have no choice but to use sampling: they buy a smaller number
of bonds that approximate the overall
characteristics of the
index (average term, coupon, duration, etc.).
The
index might have 100
bonds that fall into a given bucket, but we could select just a few
bonds to help meet the risk
characteristics of that bucket for the portfolio.
The percentages
of the Portfolio's assets allocated to each Underlying Fund are: Vanguard Total
Bond Market II
Index Fund 14 % Vanguard Total International
Bond Index Fund 5 % Vanguard Short - Term Inflation - Protected Securities
Index Fund 6 % Vanguard Federal Money Market Fund 75 % Through its investment in Vanguard Total
Bond Market II
Index Fund, the Portfolio indirectly invests in a broadly diversified collection
of securities that, in the aggregate, approximates the Bloomberg Barclays U.S. Aggregate Float Adjusted
Index in terms
of key risk factors and other
characteristics.
Instead,
bond ETF managers use a «sampling» approach where they try to replicate the risk and return
characteristics of the
index using a smaller portfolio
of available
bonds.
Tracking a large
bond index is difficult and expensive, so
index funds pegged to the DEX Universe always use «representative sampling,» selecting a smaller
of number
bonds with similar overall
characteristics.
That being the case, ETF managers attempt to reflect the risk and return
characteristics of popular
bond indices by sampling a basket
of liquid securities that trade frequently and closely track the
index.
Bonds of an
index with similar
characteristics can be grouped together and will have similar risk attributes.
The percentages
of the Portfolio's assets allocated to each Underlying Fund are: Vanguard Total
Bond Market II
Index Fund 70 % Vanguard Total International
Bond Index Fund 17.50 % Vanguard Institutional Total Stock Market
Index Fund 8.75 % Vanguard Total International Stock
Index Fund 3.75 % Through its investment in Vanguard Total
Bond Market II
Index Fund, the Portfolio indirectly invests in a broadly diversified collection
of securities that, in the aggregate, approximates the Bloomberg Barclays U.S. Aggregate Float Adjusted
Index in terms
of key risk factors and other
characteristics.