Impact of Length or Relevance of Questionnaires on Attrition in Online Trials: Randomized Controlled Trial

¹ Faculty of Public Health & Policy, London School of Hygiene & Tropical Medicine , London , GB

² MRC General Practice Research Framework , London , GB

³ MRC Biostatistics Unit, Institute of Public Health , Cambridge , GB

⁴ E-health Unit, Research Department of Primary Care and Population Health, University College London, London , GB

⁵ MRC Biostatistics Unit, Institute of Public Health , London , GB

⁶ Department of Health Sciences and HYMS, University of York , York , GB

⁷ E-health Unit, Research Department of Primary Care & Population Health, University College London, London , GB