Effect of telephone follow-up on retention and balance in an alcohol intervention trial

Telephone follow-up is not currently recommended as a strategy to improve retention in randomized trials. The aims of this study were to estimate the effect of telephone follow-up on retention, identify participant characteristics predictive of questionnaire completion during or after telephone follow-up, and estimate the effect of including participants who provided follow-up data during or after telephone follow-up on balance between randomly allocated groups in a trial estimating the effect of electronic alcohol screening and brief intervention on alcohol consumption in hospital outpatients with hazardous or harmful drinking.

Trial participants were followed up 6 months after randomization (June-December 2013) using e-mails containing a hyperlink to a web-based questionnaire when possible and by post otherwise. Telephone follow-up was attempted after two written reminders and participants were invited to complete the questionnaire by telephone when contact was made.

Retention before telephone follow-up was 62.1% (520/837) and 82.8% (693/837) afterward: an increase of 20.7% (173/837). Therefore, 55% (95% CI 49%-60%) of the 317 participants who had not responded after two written reminders responded during or after the follow-up telephone call. Age < 55 years, a higher AUDIT-C score and provision of a mobile/cell phone number were predictive of questionnaire completion during or after telephone follow-up. Balance between randomly allocated groups was present before and after inclusion of participants who completed the questionnaire during or after telephone follow-up.

Telephone follow-up improved retention in this randomized trial without affecting balance between the randomly allocated groups.