Study design and participants

Data were obtained from the GB Kantar Fast-Moving Consumer Goods panel, a consumer panel of food and beverages purchased by households in Great Britain and brought into their home. Our data set covers purchases made during 2014–2017. The panel uses an open-panel design, comprising of 31 000 to 34 000 households annually. Households are recruited via stratified sampling, with quotas set for region, household size, age of main shopper, number of children and occupation. Households record purchases continuously throughout the year and are offered incentives to remain in the panel in the form of vouchers with an average value of £100 per household per year. Panel retention is high – participating households in 2014 had median follow-up time of 2·6 years. Approximately 3000–4000 new households are enrolled each year to maintain national representativeness. Panellists provide socio-demographic data when joining the panel (including age, sex, occupation, ethnicity, household composition, income and others) followed by annual updates.