These plots show this relationship San Mateo County houses using color coding which generally highlights changes in the market. More San Mateo County homes being sold over list price is a very good indicator of rising home prices. More homes being sold under list price is a very good indicator of falling home prices.

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Looking at price per square foot gives a partial adjustment for differences between sizes of houses. Furthermore if you look at the average size of a San Mateo County house sold you will see that it varies with time. Part of the variation is due to the random nature of which houses are being sold but there tends to be a increase in the size with time because when a house is replaced with a newer house, the newer house is almost always larger.