Fieldwork: Letters and reminder regime

One of the biggest challenges when conducting self-completion surveys is maximising the survey response rate – we aimed to do this through effective design of materials and optimising our mail-out strategy.

We adopted a push-to-web approach, and the following mailings were despatched monthly (with the day of the week that mailings land varying):

1. Letter sent to all sampled addresses inviting up to two adults to go online and complete the online questionnaire (C5 white envelope, 2nd class postage);
    
2. A reminder letter was sent one to two weeks after the first invitation to non-responding addresses and addresses where only one adult had completed the online questionnaire but not a second adult (presence of an eligible second adult was determined in the first questionnaire - C5 white envelope, 2nd class postage);
    
3. Another reminder letter was sent one to two weeks after the first reminder letter to non-responding addresses and addresses where only one adult had completed the online questionnaire but not a second adult (presence of an eligible second adult was determined in the first questionnaire); this mailing included one or two postal questionnaires (C4 white envelope, 2nd class postage);
    
4. A final reminder letter was sent two weeks after the second reminder letter to a randomly selected half of the non-responding addresses and addresses where only one adult had completed the online or paper questionnaire but not a second adult (presence of an eligible second adult was determined in the first questionnaire). Note that in only a small number of cases are paper questionnaires received back in time to feed into the mailing 4 selection (C5 white envelope, 2nd class postage).