FHRS Audit Technical report 2022: Sampling

For both the audit and telephone survey of food businesses, the sample was obtained from the FSA’s FHRS database. The database initially provided by the FSA included multiple markers such as the business address, FHRS rating, business type, and local authority. It is important to note that the FHRS database is subject to change between the point when the sample is drawn and fieldwork timings due to some food businesses waiting for their appeal during this time.    

The initial dataset received from the FSA on 13th September 2022 contained 371,621 food businesses. This sample was processed to exclude food businesses that were ineligible for the research. Specifically, food businesses were excluded if they had not yet been inspected and issued with an FHRS rating, if they operated in a premise that were not publicly accessible and if they were a mobile food business. ^{(footnote 1)}

From this sample frame we drew 26,914 food businesses, stratified by country, outlet type and FHRS rating to broadly reflect the underlying population of food businesses. Food businesses in England were stratified by region also. Sampled businesses in England broadly fell out in line with the underlying local authority/district council populations although we did not incorporate this into the sample stratification. ^{(footnote 2)} Businesses in Northern Ireland and Wales, takeaways and sandwich shops and those with a food hygiene rating of three or less were oversampled to ensure that robust results could be produced for each sub-group.  

As there are no contact details available on the FHRS database, IFF Research undertook a process of matching telephone numbers to the database. This was achieved by using an external data supplier (REaD Group), who mapped the business names and addresses to their database of telephone numbers via internal desk research. This process yielded a starting sample of 9,583 food businesses.  

The sample frame for the 2022 wave of the FHRS Audit and Survey differed slightly from previous waves as Bed & Breakfasts were excluded from the sample of accommodation businesses due to access issues in previous audits, and home caterers were included in the sample of catering businesses for the telephone survey. Although the 2022 sample frame differs slightly from the 2021 sample frame, there are no concerns about the comparability of data as Bed & Breakfasts and home caterers only make up a small proportion of their respective outlet type groupings.   

From the starting sample of 9,583, a smaller number (4,093) of business sites were selected at random in line with the country, sector and rating targets. Less sample was required for the audit fieldwork as the ability to conduct covert audits was not reliant on the consent of the business. Kitchens without physical premises were not included in the audit. Food businesses considered inaccessible to the public (e.g. staff canteens) were also not intended to be audited, although some were erroneously included in the drawn sample, and two audits of staff canteens were subsequently conducted. ^{(footnote 3)}

^{Tables 2.1 to 2.3 present the profile of the starting sample (9,583) of eligible and usable food businesses for audit and telephone fieldwork in terms of country, outlet type and FHRS rating.}