Method version briefing-1.0
How briefing figures are calculated
Each briefing fixes a reporting window, a station cohort and a table of evidence. It is reviewed before publication and keeps its published figures.
Reporting window and price movements
The stated window includes its start and excludes its end. For each station and fuel, we retrieve the preceding history record, then compare each subsequent record in order. Different accepted prices count as movements. Unchanged confirmations and first observations do not. An invalid price breaks the chain; the next valid entry establishes a new baseline.
One station can have several movements, or both a rise and a fall. Counts of movements and counts of distinct stations are separate. The timestamp is the source's effective time, not when the importer received it. Five-minute feed checks cannot guarantee every intermediate pump change is retained.
Station cohort and prices at the cutoff
We use the currently active, open inventory with the normal public postcode, coordinate and test-data checks. These site classifications describe preparation time; we do not claim to reconstruct historical ownership, closures or boundaries.
The latest history price strictly before the cutoff is carried forward if it falls within the preceding 14 days and the accepted range of 50p to 300p per litre. Each qualifying site has one equal vote. No new event means no observed change; a price excluded by the age rule is not necessarily incorrect.
This historical cutoff calculation differs from the current reported-price cards, which can also use newer source confirmations. It also differs from the separately frozen weekly historical series. Always use the measure named in the briefing.
Comparisons and threshold shares
Changes in average price compare the same stations with a valid price at both endpoints. The denominator for a threshold share is the number of sites with a qualifying price at the cutoff. “£2 or more” means at least 200.0p per litre, not 199.9p.
Movement counts cover the qualifying inventory over the whole window. Cutoff counts include only sites with a valid, sufficiently recent final price, so the number of sites with a movement can exceed the closing price count.
Postcode-area rows require at least 20 reporting stations and 20 matched stations. Postcode areas are not city or council boundaries. Standard diesel excludes premium diesel; the retained field can contain a B10 fallback where the feed did not supply standard B7.
Publication, corrections and limits
A prepared package is a draft until editorial review and publication. Published briefings retain their data and cutoff. A correction creates a separate dated page explaining the change, with links between versions. Later source reports may change a newly prepared analysis without changing an earlier published edition.
The data does not measure fuel sales, purchases or the price of a typical litre sold. It cannot by itself establish why prices changed, a retailer's motives or a comparable all-time record from another provider's series.