title: Two controlled trials to increase participant retention in a randomized controlled trial of mobile phone-based smoking cessation support in the United Kingdom.
abstract: BACKGROUND
  Loss to follow-up of trial participants represents a threat to research validity. To date, interventions designed to increase participants' awareness of benefits to society of completing follow-up, and the impact of a telephone call from a senior female clinician and researcher requesting follow-up have not been evaluated robustly.
  
  
  OBJECTIVE
  Trial 1 aimed to evaluate the effect on trial follow-up of written information regarding the benefits of participation to society. Trial 2 aimed to evaluate the effect on trial follow-up of a telephone call from a senior female clinician and researcher.
  
  
  METHODS
  Two single-blind randomized controlled trials were nested within a larger trial, Txt2stop. In Trial 1, participants were allocated using minimization to receive a refrigerator magnet and a text message emphasizing the benefits to society of completing follow-up, or to a control group receiving a simple reminder regarding follow-up. In Trial 2, participants were randomly allocated to receive a telephone call from a senior female clinician and researcher, or to a control group receiving standard Txt2stop follow-up procedures.
  
  
  RESULTS
  Trial 1: 33.5% (327 of 976) of the intervention group and 33.8% (329 of 974) of the control group returned the questionnaire within 26 weeks of randomization, risk ratio (RR) 0.99; 95% confidence interval (CI) 0.88-1.12. In all, 83.3% (813 of 976) of the intervention group and 82.2% (801 of/974) of the control group sent back the questionnaire within 30 weeks of randomization, RR 1.01; 95% CI 0.97, 1.05. Trial 2: 31% (20 of 65) of the intervention group and 32% (20 of 62) of the control group completed trial follow-up, RR 0.93; 95%CI 0.44, 1.98.
  
  
  CONCLUSIONS
  In presence of other methods to increase follow-up neither experimental method (refrigerator magnet and text message emphasizing participation's benefits to society nor a telephone call from study's principal investigator) increased participant follow-up in the Txt2stop trial.
authors.affiliation: Health Protection Agency, London, UK. ettore.severi@hpa.org.uk
authors.forename: Ettore
authors.initials: E
authors.lastname: Severi
authors.forename: Caroline
authors.initials: C
authors.lastname: Free
authors.forename: Rosemary
authors.initials: R
authors.lastname: Knight
authors.forename: Steven
authors.initials: S
authors.lastname: Robertson
authors.forename: Philip
authors.initials: P
authors.lastname: Edwards
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Hoile
mesh_terms: D000328:Adult; D040421:Cell Phone / Q000295:instrumentation*; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design; D012306:Risk; D016540:Smoking Cessation / Q000379:methods*; D000074606:Smoking Prevention; D012944:Social Support; D011795:Surveys and Questionnaires; D013997:Time Factors; D006113:United Kingdom