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Methodology — Gera Hygiene Trend Index (GHTI)

Published: 2026-06-20 · Data source: Food Standards Agency FHRS (OGL v3.0)

1. What the GHTI measures

The Gera Hygiene Trend Index (GHTI) is defined as the year-on-year net change in the percentage of 5-star (Very Good) FSA-rated food establishments in a local authority area:

GHTI = (5-star % this year) − (5-star % previous year)

A positive GHTI means more establishments achieved top-rated hygiene than the year before. A negative value indicates a decline. The index is expressed in percentage-point terms and requires two annual snapshots of the same FSA dataset to compute.

2. Data source

Source
Food Standards Agency (FSA) — Food Hygiene Rating Scheme (FHRS)
Download URL
https://ratings.food.gov.uk/open-data — “All local authorities (English)” bulk CSV. No registration or API key required.
Licence
Open Government Licence v3.0 (OGL v3.0). Contains public sector information licensed under the Open Government Licence v3.0.
Coverage in this dataset
120 English local authorities · 291,282 rated establishments · as of June 2026
National 5-star baseline
75.9% of rated establishments hold a 5-star FSA rating across the 120 local authorities in this dataset (as of June 2026).

3. Historical-snapshot availability — honesty disclosure

Computing GHTI trend figures requires two annual snapshots of the FSA bulk CSV (e.g. a 2023 snapshot and a 2024 snapshot). The FSA open-data portal publishes one live snapshot — the current ratings for every establishment, refreshed daily. No 2022 or 2023 historical archive is available for key-free download (verified 2026-06-20 against the portal at ratings.food.gov.uk/open-data).

Therefore, no GHTI trend values are computed on these pages. Fabricating or estimating a historical 5-star percentage would violate our honesty bar and the OGL licence conditions. What is published instead:

  • Real current-state 5-star percentages, rating distributions, and GHSI scores from the June 2026 FSA bulk CSV for 120 English local authorities.
  • The GHTI formula and methodology, so the index can be computed once a second annual snapshot becomes available.
  • A guide to monitoring FSA hygiene trends, including how to snapshot the bulk CSV yourself.

When Gera archives a second annual FSA snapshot, GHTI trend values will be added to these pages with full source attribution and date transparency.

4. Gera Hygiene Standard Index (GHSI)

Because GHTI trend values are not yet computable, each local authority page also shows the Gera Hygiene Standard Index (GHSI) — the current-state metric against which future trend changes will be measured.

GHSI = 5-star % − (0-star % × 5)

The penalty term (zero-star × 5) gives additional weight to the most severe hygiene failures (Urgent Improvement Necessary), which carry a public-health risk. GHSI ranges conceptually from −∞ to 100, though in practice the 120 LAs in this dataset score between 34.8 and 95.5. The national baseline is 75.9% 5-star, giving a national GHSI of approximately 75.9 (assuming ~0% zero-star nationally).

5. Exclusions and scope

  • Scotland uses the FHIS (Food Hygiene Information Scheme) — pass/fail, not the 0–5 FHRS scale. Scottish authorities are excluded from GHSI/GHTI calculations to avoid mixing incompatible rating systems.
  • Establishments with an “Awaiting Inspection” or “Exempt” status are excluded from all percentage calculations (they are not in the denominator).
  • Local authorities with fewer than 100 rated FHRS establishments are excluded to avoid unreliable small-sample percentages.
  • This dataset covers the top 120 English local authorities by establishment count. Welsh authorities that use FHRS (not FHIS) are in principle includable but are not in the current cut.

6. Reproducibility

To reproduce the figures on these pages:

  1. Download the bulk CSV from https://ratings.food.gov.uk/open-data — no key required.
  2. Filter rows where SchemeType = FHRS.
  3. Exclude rows where RatingValue is AwaitingInspection or Exempt.
  4. Group by LocalAuthorityName. Count total, count where RatingValue = 5, count where RatingValue = 0.
  5. Compute: fivestar_pct = (fivestar / total) × 100
  6. Compute: zero_pct = (zero / total) × 100
  7. Compute: GHSI = fivestar_pct − (zero_pct × 5)

Every figure on the local authority pages in this cluster traces directly to this calculation applied to the FSA bulk CSV downloaded on 19 June 2026.

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