I have heard it over and over; people in the financial media presenting information on the bond markets continually make erroneous assumptions about the relationship of mortgage interest rates with US Treasury Bond and Note prices.  This happens because these financial reporters may understand the bond markets in general but they are not mortgage experts and do not fully understand how mortgage interest rates are determined.  For example, the bond market reporters mistakenly tie mortgage rates to the performance of the US 10-year Treasury Note on a routine basis.  You see this happen all the time.  In reality, mortgage interest rates and the intra-day re-pricing that occur are determined from the performance of mortgage-backed securities (MBS or mortgage bonds), not US 10-year Treasury Notes.

The table below illustrates data for the time period between July 10 and August 10, 2007.  During the 24 trading days, the two securities moved in the same direction 20 times but actually moved in the opposite direction four times.  If you were watching the US Treasury notes to determine the way mortgage pricing would respond, you would have had a couple of pretty big misses on some of those days (see charts below).  Moreover, on the 20 days when they did move in a similar direction, the relative change was close on only 5 of the 20 dates.  In fact, the two securities behaved closely on only 6 of a total of 24 trading days (just 25%).  The relative change between the two was never exact!  On a majority of the 20 days when the two instruments moved in a like direction, the difference in the amount of the move was significantly different.  This could have caused client confusion, client frustration and poor or incorrect guidance by the originator to his or her customer.