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Effects of estimated completion time and unconditional gift certificates on questionnaire response
  1. Marleen M H J van Gelder1,2,
  2. Pauline M Geuijen1,
  3. Jeanne H M de Vries3,
  4. Nel Roeleveld1,4
  1. 1Department for Health Evidence, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
  2. 2Radboud REshape Innovation Center, Radboud University Medical Center, Nijmegen, The Netherlands
  3. 3Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands
  4. 4Department of Paediatrics, Radboudumc Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, The Netherlands
  1. Correspondence to Dr Marleen MHJ van Gelder, Department for Health Evidence (HP 133), Radboud University Medical Center, P.O. Box 9101, Nijmegen 6500 HB, The Netherlands; Marleen.vanGelder{at}

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Obtaining a high response rate is important to reduce selection bias. Some strategies, including prenotification, monetary incentives and shorter questionnaires, may increase response rates, whereas other strategies have no or unclear effects.1 We determined whether the estimated completion time and/or an unconditional gift certificate affect questionnaire response.

Pregnant women participating in the PRIDE Study were asked to fill out a postal food frequency questionnaire (FFQ) after completing the web-based baseline questionnaire.2 We employed three strategies to increase response rates in succession: (1) underestimation of completion time (10–15 min) without offering incentives, (2) underestimation of completion time with an unconditional €5 gift certificate for an online store and (3) correctly estimated completion time (20–30 min) with …

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