Sithi household survey

Privacy notice

This notice explains what the Sithi household survey collects, why, how long it is kept and your rights. The survey collects information about health, which the law treats as special category data, so we keep it to the minimum.

Who we are

The data controller is Neurithmetic Limited, trading as Sithi, registered in England & Wales no. 15177502, The Courtyard, Shoreham Road, Upper Beeding, Steyning, West Sussex, BN44 3TN. Neurithmetic Limited is registered with the Information Commissioner's Office, registration number ZC180071. Contact: hello@sithi.net.

What we collect

• About you: your age group, your sex if you choose to give it and the letters at the start of your postcode (for example BN). From the letters we work out your region.
• About your household: how many people live with you in each of four age groups. No names, no dates of birth.
• Each week: for each person who was unwell, their age group, which of ten listed symptoms they had and whether the illness came on suddenly; whether anyone tested positive for COVID-19 or flu; whether anyone missed work, school or nursery; and whether anyone contacted a GP, NHS 111 or a pharmacy. The date of your answer is stored, not the time.
• A random code that recognises your household when you return. It is created when you first answer and kept in your browser's local storage on your device. We store only a scrambled (hashed) version of it.
• Your email address, only if you ask for reminders. It is stored in a separate database from the answers, with no code or other link to them, so we cannot tell which answers belong to which email address.

We do not collect names, free text, precise locations or IP addresses with your answers. Our web server does not log the requests that carry survey answers or reminder sign-ups. To stop abuse we count requests from each connection for a short time; this count is held in memory only, uses a scrambled form of the address that changes every day and is never stored with your answers. The survey does not use cookies, analytics or tracking.

Why we use it and our lawful basis

We use your answers only to produce anonymous weekly statistics for the Sithi Illness Index and related analysis on sithi.net. Our lawful basis is your consent (UK GDPR Article 6(1)(a)) and, because the answers are health information, your explicit consent (Article 9(2)(a)), which you give by ticking the separate consent box. Reminder emails are sent on the basis of your consent (Article 6(1)(a)).

We never use the answers to contact you, to give medical advice, for marketing or to make decisions about you. We do not sell or share them. Only weighted totals are published, and any figure based on fewer than 10 responses is suppressed.

Where it is kept and who can see it

Answers and email addresses are kept on our own server, hosted by Hostinger, in separate files that only the survey service and Sithi's administrators can read. Reminder emails are sent through our email host, Hostinger. No other organisation receives the data.

How long we keep it

• Weekly answers are deleted 24 months after the week they cover.
• If your household does not answer for 12 months, its details and all its answers are deleted.
• Reminder addresses are deleted when you stop the reminders. Unconfirmed reminder requests are deleted after seven days.
• Published statistics are anonymous and are kept indefinitely.

Your rights

You can withdraw your consent at any time. The quickest way is the "Delete my household's answers" button on the survey page, which deletes your household's details and every answer straight away. Every reminder email has a link to stop reminders and delete your address.

You also have the right to see, correct or delete your data, to restrict or object to its use and to receive a copy of it. Because we do not know who you are, we can find your answers only with your household's private link; please include it if you write to us at hello@sithi.net. If you are unhappy with how we have handled your data you can complain to the Information Commissioner's Office at ico.org.uk.

Adults only

The survey is for people aged 18 or over. Children are counted only as members of a household, by age group, never individually named.

Last updated 24 October 2026. A data protection impact assessment has been carried out for this survey.