The three families
National official statistics, which produce the construction price index and housing market data.
Publications of the public housing observatory, covering the property and land market.
Professional sources, specialist publishers and market participants, which publish price ranges per square metre.
These three families differ in status, reliability and subject matter. Confusing them leads to citing a commercial estimate as an official figure.
| Family of source | What it provides | Reliability |
|---|---|---|
| Official statistics | Series and official indices | The highest |
| Professional publication | Price ranges by building type | Good, scope to be checked |
| Sales listing | Asking prices | Indicative only |
What each family covers
Official statistics cover movements, not price levels per project. The index says how much prices have moved, not what a house costs.
The public observatory covers transactions and the market, with detail varying by segment.
Professional sources cover price levels, which official sources do not, but without official status and often with imprecise scopes.
No single source provides what a client needs, which means combining them while knowing the limits of each.
The statistical gap to know about
A rarely flagged and yet decisive point.
The public observatory does not publish detailed statistics on house sale prices, for want of sufficient data on that segment.
The detailed statistics available relate mainly to apartments.
The consequence is direct: anyone seeking a reference price for a house will find no detailed official figure, and will have to fall back on professional sources or less granular transaction data.
That gap explains part of the divergence between published figures, each source reconstructing the missing segment in its own way.
The hierarchy to respect
Four levels, in decreasing order of reliability. They range from official statistics to sales listings.
The official text or primary statistical publication, always to be preferred.
The publication of the competent public body, notably for market data.
The identified professional source, usable for price levels, provided its date and scope are cited.
The quotation, which remains the only figure genuinely specific to the project, and which prevails over all the above for estimating a given project.
A secondary source must never be cited in place of an available primary source, particularly in tax matters, where divergence between sources is frequent.
Reading precautions
Four checks, on any figure used.
The date, given the publication lag of the official series.
The scope, notably the inclusion or exclusion of land and tax.
The segment, house or apartment, new or existing, these markets not moving together.
The status of the source, official or professional, which determines the weight to give it.
What this means for a professional
Four rules.
Cite the source, date and scope of any figure used in a document issued.
Flag the gap on houses where a client expects an official figure that does not exist.
Never present a professional range as public statistical data.
Return to the quotation as soon as the project is sufficiently defined, no general source replacing an offer.
This article reflects the state of publications at the date of checking and serves professional orientation. It does not replace direct consultation of the sources cited.