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Table 2 Changes made in each wave of the study

From: Increasing questionnaire response: evidence from a nested RCT within a longitudinal birth cohort study

WaveTime periodDescription of questionnaire distributionChanges between waves
1st attempt2nd attempt
Wave 14 monthsQuestionnaire and cover letter (V1) sent via email or post (stamped addressed envelope included)Questionnaire resent via post-
Wave 24 monthsQuestionnaire layout updated and cover letter (V2), sent via email or post (stamped addressed envelope included)Questionnaire resent via postCover letter updated to utilise behaviour change techniques designed to increase response, free pen included, questionnaire updated
Wave 34 monthsQuestionnaire and cover letter (V2), sent via email or post (stamped addressed envelope included)Reminder by:
Postcard
Telephone call
Questionnaire resent
RCT conducted for those who did not complete the questionnaire on the first send out to determine if one reminder was more effective or reduced bias