Moving from Market Opacity to Methodological Opacity: Are Web Data Good Enough for French Property Market Monitoring?

Abstract

The big data era facilitates the use of new online data sources in both academic and professional fields: In real estate, for instance, private Web data such as online property price estimates have become commonly used sources for investigating property markets. The quality of such data, however, has not been routinely assessed. This article therefore statistically analyzes the quality of Web data for mapping local property prices. To do so, it compares property estimates drawn from ten Web sites and property prices calculated from the Demande de Valeurs Foncières central state tax services database for a stratified sample of sixty French municipalities. This study reaches a paradoxical conclusion and theorizes it as a shift from market opacity to methodological opacity: Although it has become easier to obtain property price estimates at a local level, this commodified form of information is hardly suitable for geographical research on local property markets due to its varying, unpredictable quality. The partially disclosed or even missing metadata and methodologies make it indeed impossible to identify the sources of biases (sampling or stock vs. flow effects). The article shows that this methodological opacity is directly linked to the strategic role of copyrighted information in a context of property market reintermediation.