How do the monthly datasets for NAR "existing home sales" and Census "new home sales" differ?
Existing-home sales differ from the U.S. Census Bureau's series on new-home sales based on the timing of record of sale.
The U.S. National Association of Realtors (NAR) "existing home sales" dataset is based on transaction closings, in which the house is usually ready for occupancy. It is based on a much larger sample (sales are usually an 85/15 split between existing and new).
Conversely, the U.S. Census Bureau's "new home sales" dataset is based on contracts or the acceptance of a deposit, and the house can be in any stage of construction, from "not started" to "fully complete." Also, it is subject to large prior-month revisions.
It is not uncommon for the two series to move in opposite directions in the same month.
Existing Home Sales
Existing Home Sales - Annual
New Home Sales (C25)