Zillow vs DataQuick

by Christine Braun | Oct 27, 2015

The Age of Information has spurred an explosion of data and sources from which to collect these data, leaving researchers to debate over which sources and methods are preferable to others. Data from the housing market are no exception to such debate, with several sources to choose from: Zillow, Case-Shiller, DataQuick (DQ) and California Association of Realtors (CAR). So why do we prefer Zillow for our data on housing prices?

Zillow Research Data provides timely housing data for very specific geographic areas (neighborhoods, zipcodes, cities, counties, MSAs, States, and the U.S.). Although prices may not be entirely accurate for any one particular home, Zillow provides a Home Price Index (ZHVI). This index tracks the monthly median home value in a particular geographic area based on estimated home values for all homes within the area, not just for those that have sold; therefore, giving a more accurate snapshot of home values in a particular region. Read more about the methodology used to create the ZHVI at: ZHVI methodology.

How does the ZHVI compare to DataQuick? DataQuick offers monthly data on the number of sales and median sales price of new homes and re-sales, for single-family homes and condos. For large housing markets with high turnover, these statistics follow a similar pattern to ZHVI with large declines beginning in 2008 and a slow recovery beginning around 2012. For large housing markets the DataQuick statistics are less volatile as they are composed of more sales. The largest three housing markets in the county are Santa Maria (13,309 sales in 2014), Santa Barbara (1,223 sales in 2014), and Lompoc (531 sales in 2014).

Santa Maria

Santa Barbara


Smaller markets such as Carpinteria (126 sales in 2014) are subject to large outliers in months with fewer sales. Although the DataQuick statistics are volatile for these markets, the trend of the data matches Zillow closely. Since the ZHVI is composed of estimated home values for all homes, not only those that have sold within the month, it is less subject to the effects of large outliers. Read more about how ZHVI compares to other sources of data at: ZHVI vs other housing data.