Sithi Illness Index
Corrections and changes
Published figures are not changed quietly. If we correct a figure or change the method, it is recorded here with the date, what changed and why. Corrections are also flagged in the downloadable history.
| Date | Type | What changed |
|---|---|---|
| 24 October 2026 | Method change (version 2.0) | Coughs, colds and flu now uses a new method: last week's UKHSA figure, adjusted for last week's change and for this week's searches in England for "chest infection", "chesty cough" and "cough". The syndromic input and the earlier search terms are no longer used for this figure. The reason: in testing, version 1.0 was further from UKHSA's figure for the week than simply repeating last week's figure (21.1 against 16.7 points on average in the held-back 2025/26 winter). Version 2.0 was 8.1. Details are on the methods page. Sickness bugs keeps the version 1.0 method, but its back-calculated history now uses the norovirus figure actually available on a Tuesday (two weeks old), as the live build already did, and the comparison on the methods page has been corrected. The whole back-calculated history has been worked out again with version 2.0. The figures first published on 24 October for the week to 18 October are restated: coughs, colds and flu from 59 to 48 and sickness bugs from 48 to 47. The version 1.0 history remains available as index-history-v1.csv. |
| 24 October 2026 | Launch | The index is published for the first time, labelled experimental, with method version 1.0. The weekly history before this date is back-calculated using the same method and the data as published by 24 October 2026; it is marked "back-calculated" in the CSV. The household survey opens on the same day and is shown as "panel: building" until it has 300 responses in a week. Weights: survey 40%, Google Trends 20%, UKHSA syndromic 20%, UKHSA laboratory and hospital 20%. |
To report a possible error, email hello@sithi.net with the week and the figure concerned.