by Calculated Risk on 6/30/2010 05:47:00 PM

CR Note: How the NAR calculates existing home inventory is a bit of a mystery. Housing economist Tom Lawler has been tracking inventory several different ways. The following post is from Tom Lawler:

This morning there were 3,973,439 residential listings on realtor.com, up 1.6% from late May and up 0.3% from a year ago. Listings in California, which declined sharply during 2009, were up 2.3% on the month and up 7.4% from a year ago. States with especially large monthly increases in listings including Washington (14.5%, after an 8.4% drop in May – Washington data are whacky!), Alaska (5.1%), Maine (4.9%), and Colorado (4.3%). Florida listings were up 0.3% on the month but down 9.5% from a year ago.

Click on graph for larger image in new window.

I’m not sure how often realtor.com listings by states are “refreshed,” or whether the updates are identical across states. However, the realtor.com data appear to “synch up” better to reports from various MLS than do the monthly National Association of Realtor data – which often displays monthly swings completely out of whack with the various “inventory trackers” that I and others follow. The NAR wasn’t willing to give me details of its methodology, but it apparently uses the sample data from various realtor associations/boards/MLS, and it may estimate the national totals with gross-ups based on “months’ supply.” Whatever the case, the monthly NAR numbers appear to have “spurious volatility” unrelated to actual swings in listings.

CR Note: This seems to suggest an increase in inventory in June. Using Realtor.com isn't perfect, but it is a consistent and transparent method.