Treasury Index
This is an index that uses treasury bills yields to generate a percentage. This percentage (interest rate) is used frequently for determining the current mortgage rates.

Further Info :

An index that is used to determine interest rate changes for certain adjustable-rate mortgage (ARM) plans. It is based on the results of auctions that the US Treasury holds for its Treasury bills and securities or is derived from the US Treasury's daily yield curve, which is based on the closing market bid yields on actively traded Treasury securities in the over-the-counter market.

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