Impact and Costs of Incentives to Reduce Attrition in Online Trials: Two Randomized Controlled Trials

Zarnie Khadjesari   ^{1 †} ;   Elizabeth Murray   ^{1 †} ;   Eleftheria Kalaitzaki   ^{2 †} ;   Ian R. White   ^{3 †} ;   Jim McCambridge   ^{4 †} ;   Simon G. Thompson   ^{3 †} ;   Paul Wallace   ^{1 †} ;   Christine Godfrey   ^{5 †}

¹ E-health Unit, Research Department of Primary Care and Population Health, University College London, London, GB

² MRC General Practice Research Framework, London, GB

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

⁴ Centre for Research on Drugs and Health Behaviour, London School of Hygiene & Tropical Medicine, London, GB

⁵ Department of Health Sciences and HYMS, University of York, York, GB