Why Measures of Existing Home Inventory appear Different

There is a significant difference between measures of inventory, and this is leading to some confusion.
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Here is a graph comparing the year-over-year change in Realtor.com’s active inventory, the NAR’s inventory, and Realtor.com inventory including pending sales. Note that the blue line (NAR) and dashed black line (Realtor including pending sales) track.

As Lawler noted, including pending sales understated the decline in active inventory in 2020 and 2021, and is now understating the increase in active inventory.

But what about Redfin? Redfin takes a very different approach. Their active inventory number for any month includes homes that came on the market and sold quickly during the month, whereas the other measures are a snapshot at the end of the month (or week).