This is the first time the IP has approached a new sample for a web survey. This experiment is only within this new sample, taken at IP11. It focuses on different ways of asking for the participation of other household members and with different ways of introducing the CAPI follow-up phase. Thus, the 840 web-first addresses were randomly allocated to four groups of 210 addresses each: two ways of asking for the participation of other household members were crossed with two different ways of introducing the CAPI follow-up phase.
For households being informed of other household member participation in the advance letter, there was a £10 unconditional incentive and a promise of an additional £15 for each person in the household (16+) who completed the questionnaire online within three weeks. There was a reminder letter after 7 working days, again mentioning the £15 conditional incentive and the deadline. Second reminder letter after 15 working days.
Upon completion of the household grid, if there is more than one adult in the household a screen conveys a message along the lines of “We would like to invite <name> to take part in the survey too. They too will receive £15 for doing so by <date>. Please either enter their email address (we will email them their own personal invite) or click here to print an invitation letter with their own unique entry code.”
For households not being informed of other household member participation in the advance letter, there was a £10 unconditional incentive and a promise of an additional £15. Reminder letters were as above. Upon completion of the household grid, the screen regarding other household members appeared, as above.
For households informed of the interviewer follow-up aspect in the invitation letter, the advance letter also stated that if they were unable to participate online, there would be an opportunity to be visited by an interviewer instead. There was a reminder letter after 7 working days, again mentioning the £15 conditional incentive and the deadline additionally mentioning the interviewer visit option. Households not being informed of this interviewer follow-up option did not have this information in the advance or 7-day reminder letters. For all groups, the second reminder letter sent after 15 working days announced that an interviewer would call and that each person who took part, either face-to-face or online, would receive £10.
Further, for all groups: Reminder letters were sent to the household, if no response yet. If the grid had been completed and at least one individual had not yet responded, the additional persons were sent an invitation letter appropriate to their group. Individuals who received the invitation letter at the first reminder stage received a personal second reminder if they had not yet responded. Individuals for whom the grid was completed subsequent to the first reminder stage received an invitation letter at the second reminder stage. The allocation of respondents for this experiment is controlled by the following variable:
ff_invitew11 on record k_hhsamp_ip:
1 Inform of other HH members’ participation, not of interviewer follow-up option
2 Do not inform of other HH members’ participation, not of interviewer follow-up option
3 Inform of other HH members’ participation, inform of interviewer follow-up option
4 Do not inform of other HH members’ participation, inform of interviewer follow-up option
