In the March 2012 rebalancing a significant number of bonds that were eligible for the index but were being excluded because of a technical error were added to the index. The average duration of all bonds in the index weighted by market value. FINRA - Bloomberg Active US Corporate Bond Indices are comprised of the active (most frequently traded) fixed coupon bonds represented by FINRA TRACE, FINRA's transaction reporting facility that disseminates all over-the-counter secondary market transactions in these public bonds. The indices are rebalanced on a monthly basis. Type NBBITR MEMB for constituent information. Index launch date: October 17, 2005.