Table 1

Purposive sampling strategy

Key demographic characteristicsMinimum participant quota per country
Eligible chronic condition*7 with
7 without
Gender8 females
8 males
Parent/guardian of child/children under 184 mothers
4 fathers
Age8 18–49
4 50–64
6 ≥65
Socioeconomic group (social grade)†7 ABC1
7 C2DE
Adults who have had ONE of the vaccines4 flu
3 tetanus
Have had tetanus and flu vaccines6
Have not had either vaccination6
  • *These include asthma, chronic obstructive pulmonary disease or bronchitis, heart disease, kidney disease, liver disease, neurological conditions, weakened immune system due to conditions such as HIV and AIDS, or as a result of medication such as steroid tablets or chemotherapy.

  • †A=higher socioeconomic group and E=lower socioeconomic group. We used country-specific occupation and income data to determine participants’ social grade.

  • ‡The urban/rural quotas for the UK and France were relaxed due to the quality and coverage of their public health systems.