Bloomberg Barclays US Aggregate Bond Index
The Bloomberg Barclays US Aggregate Bond Index (ticker: LBUSTRUU), formerly known as the Lehman Aggregate Bond Index and the Barclays US Aggregate Index, was created in 1986 with backdated history going back to 1976. The index has been maintained by Bloomberg L.P. since August 24th 2016.  The index is a predominate index benchmark for US bond investors, and is a benchmark index for many US index funds.
The Index is a composite of four major subindexes: US Government Index; US Credit Index; US Mortgage Backed Securities Index (1986); and (beginning in 1992) US Asset Backed Securities Index. The index holds investment quality bonds. The ratings are based on S P, Moody, and Fitch bond ratings. Table 3 in the appendix provides credit quality breakdowns for the index from 2005-2009. The index does not include high yield bonds. municipal bonds. inflation-indexed bonds. or foreign currency bonds. In 2010, the index held more than 8,200 bond issues.  The time line for the addition and subtraction of asset classes, as well as changes in the minimum issue size and credit quality standards for the index are included in the time line sidebar.
Milestones in the Evolution of the Bloomberg Barclays U.S. Aggregate Index
- 1/73 Inception date for Government/Corporate Index.
- 1/86 Introduction date for the Mortgage-Backed, Yankee, and Aggregate Indices, with returns and statistics calculated back to 12/31/75.
- 8/88 Liquidity constraint increased from $1 million to $25 million for corporate issues. Yankee Index absorbed into the Government/Corporate Index.
- 1/89 Published durations changed from Macaulay duration to maturity to duration to worst. Published yields changed from yield to maturity to yield to worst.
- 1/90 Liquidity constraint increased from $25 million to $100 million for government issues. Yankee sector absorbed into the Corporate Index. Title XI issues dropped from the Government Index. Asset-backed bullet issues added to the finance sector.
- 1/92 Asset-Backed Securities Index added to Aggregate Index. Balloon issues added to MBS Index. Liquidity constraint increased from $25 million to $50 million for nongovernment issues. Mobile homes dropped from MBS Index.
- 1/94 Liquidity constraint increased from $50 million to $100 million for all issues.
- 1/95 GPMs dropped from the MBS Index. Average coupons par-weighted instead of market-weighted.
- 12/97 Added stranded cost securities to the Asset-Backed Securities Index.
- 12/98 Manufactured housing securities added to the ABS Index. Quarter-coupons dropped from MBS Index. All World Bank Issues moved to supranational component of Corporate Index.
- 7/99 Liquidity constraint raised to $150 million from $100 million. ERISA-eligible CMBS added to the Aggregate Index.
- 7/00 Renamed Corporate Index to Credit. Absorbed all Yankee Corporates into their respective industry classifications. Changed the liquidity constraint on the ABS Index—old constraint: $150 million per tranche; new constraint: deal must be $500 million, tranche must be $25 million. ERISA-eligible B pieces to be included also.
- 10/03 Liquidity constraint raised to USD200mn from USD150mn. Started using the most conservative rating of Moody’s and S P to determine index eligibility instead of Moody’s only for split-rated securities.
- 7/04 Liquidity constraint raised to USD250mn/USD25mn CMBS tranche size from USD 200mn.
- 7/05 Fitch ratings added to Moody’s and S P to determine index eligibility and classification.
- 4/07 Agency Hybrid Adjustable Rate Mortgage (ARM) securities added to the index, but not eligible for the Global Aggregate.
- 1/08 U.S. MBS Fixed-Rate Balloons and U.S. ABS Manufactured Housing removed.
- 11/08 Index rebranded as Barclays Capital U.S. Aggregate Index.
- 10/09 U.S. ABS Home Equity Loans removed.
- 01/11 Covered bonds become eligible, A1A tranches are removed from the CMBS portion of the index.
- 05/12 Issuer eligibility for fixed-rate ABS no longer based on a predefined list of “eligible” issuers.
- 04/13 Loan participation notes (LPNs) eligible for the index.
- 04/14 Minimum liquidity for US MBS Index constituents raised from USD250mn to USD1bn.
- 07/14 US Agency CMBS added to the index.
The current bond asset classes comprise the index: 
The relative weighting of asset classes within the index changes over time as new asset classes are added to the index, as issuance of bonds grows and ebbs, and as market security values fluctuate. The following table shows the index sector allocation over the period 1973-2013. A breakdown of mortgage backed securities (GNMA, FHLMC, FNMA) in the index from 1978-2001 is included in the notes.
In June 2009, as a result of the 2008 financial crisis, Barclay’s announced the creation of the US Aggregate Float Adjusted Index that excludes Treasuries, agencies and MBS held in Federal Reserve accounts. 
Table. Bloomberg Barclays US Aggregate Bond Index Sector Allocation
Trailing 5 years  
The Bloomberg Barclays US Aggregate Bond Index was formulated as a market benchmark and contains thousands of illiquid bonds. Index fund managers therefore use sampling strategies when attempting to construct index funds tracking the index. Bond holdings range from approximately 800 to 1600 bonds for SPDR and Ishares ETFs; and from approximately 930 bonds (TRowePrice) to 5200 bonds (Vanguard) for bond index mutual funds. The Vanguard Bond Market ETF is a share class of the Vanguard bond market index fund.
Index funds tracking Bloomberg Barclays US Aggregate Bond Index
Dreyfus Bond Market Index Fund
Ishares Barclays Aggregate Bond ETF
T Rowe Price US Bond Index Fund
SPDR Barclays Aggregate Bond ETFE
TIAA-CREF Bond Index
Vanguard Total Bond Market ETF(Float-Adjusted
Vanguard Total Bond Market Index Fund](Float-Adjusted)
- ↑ Breakdown of mortgage backed securities in the index.
Table. Bloomberg Barclays US Aggregate Bond Index Mortgage Backed Securities 2010 forward