A couple of key points on existing home inventory:



1) Changes in inventory usually lead prices.



2) The NAR method for estimating inventory has probably led to inventory being overstated for the last few years (along with sales). It appears this discrepancy started in 2007 (or earlier), and the error has probably increased since then.



Keeping those two points in mind, here is a repeat of a graph I posted last week.



Click on graph for larger image in graph gallery.



This graph shows the year-over-year (YoY) change in reported existing home inventory and months-of-supply. Since inventory is not seasonally adjusted, it really helps to look at the YoY change.



According to the NAR, inventory decreased 4.4% year-over-year in May from May 2010. This was the fourth consecutive month with a YoY decrease in inventory. So even though inventory (and months-of-supply) is still very high, it appears that inventory is now decreasing.



However it appears the NAR is understating the decline in inventory.



A few weeks ago, Tom Lawler posted on how the NAR estimates existing home inventory. The NAR does NOT aggregate data from the local boards (see Tom's post for how the NAR estimates inventory). Sometime this summer, I expect the NAR to revise down their estimates of inventory and sales for the last few years. Also the NAR methodology for estimating sales and inventory will likely (hopefully) be changed.



While we wait for the NAR, I think the HousingTracker data that Tom mentioned might be a better estimate of changes in inventory (and always more timely). Ben at HousingTracker.net is tracking the aggregate monthly inventory for 54 metro areas.



This graph shows the NAR estimate of existing home inventory through May (left axis) and the HousingTracker data for the 54 metro areas through June. The HousingTracker data shows a steeper decline (as mentioned above, the NAR will probably revise down their inventory estimates this summer).



The third graph shows the year-over-year change in inventory for both the NAR and HousingTracker.



HousingTracker reported that the weekly average for June listings - for the 54 metro areas - declined 8.5% from last June.



Although inventory is still high, the decline in inventory will put less downward pressure on house prices and is something to watch carefully this year.



Earlier ...

• Case Shiller: Home Prices increase in April

• Update: Real House Prices and Price-to-Rent