Are you independent?
IGEDD is part of the government. It does not sell or purchase any property or property-linked service. As such, it has no interest in that property prices or sales numbers move one way or the other.
To English page : Property Market in France since 1200
To English FAQs
to French home page "Le marché immobilier depuis 1200"
To French FAQs
About the "tunnel" (in English)