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

1 For example, Foncia, one of the leading property managers in France, bought Efficity.com in 2014, and the German publishing house Axel Springer Verlag AG bought Meilleursagents.com in 2019.

2 An extraction of the DVF files became available very recently (April 2019), but these data sets remain weaker than those of the DVF central state tax services and raise problems of relational data integrity (Casanova Enault, Boulay, and Coulon Citation2019). In this article, thanks to a partnership agreement with the public land institution of the PACA region (Etablissement Public Foncier de la Région PACA), which is entitled to use the DVF files, we were able to use the original central state tax services DVF files.

3 PACA stands for Provence–Alpes–Côte d’Azur (see Figure 2). The PACA region has a population of 5 million, after strong growth in the second half of the twentieth century.

4 The municipality (commune in French) is the smallest administrative unit in France. They are very different from one another in terms of size (from less than 1 km² to more than 1,000 km²) and population (from fewer than ten inhabitants to more than 2 million inhabitants) but are all local governments with similar decentralized administrative powers.

5 The PACA region property market is distinguished by relatively high prices compared to national levels, due to a high rate of urbanization and continued popularity as a tourism destination. At a finer scale, it is nevertheless characterized by considerable spatial discontinuities, reflecting a wide range of typical French property submarkets. The PACA property market thus cannot be considered as an outlier among regional French property markets.

6 To test the quality of online data within the framework of different markets, the demographic weight of the municipalities could have been chosen as a proxy to stratify the sample. That would have led to ignoring one aspect that should play a role in data quality, however: the local intensity of the property market (the PACA region is a popular tourist destination, and some of the municipalities are considered very attractive even though they are sparsely populated; see note 5).

7 The municipalities for which the Citation2012 versus 2013 number of property transactions growth rate was not between −1.5 σ and 1.5 σ of the strata average were excluded from the sample.

8 Web site 2 is not represented in our figures because only two Web sites provide median price estimations, and one of the two was removed from the study due to insufficient data.

9 We obviously know that these new online appraisers strive above all to model the property stock value in all of its diversity. Their providing of property valuations is largely ambiguous, though: As shown in Table 1, all Web sites without exception offer “average” or “median” price references; that is, measures of a central tendency in common use. From there, we adopted this posture at face value and raised the question of whether online price estimations can be used to study actual dynamics of investment linked to the local property markets. The merit of such a naive approach in assessing online price estimations is that it highlights the central role of modeling in most of the available online price estimations.

10 It indicates that some Web sites provided price estimations closer to the actual property market dynamics of 2014, however (see Figures 3–8).

11 One of the Web sites we worked on in this article publishes a barometer of property prices on a regular basis, which is considered to be the most accurate and up-to-date information on French property markets.