Table 4 Revised protocol to improve retention

 (a) Workshop leaders and research staff were asked remind participants about the importance of the booster and follow-up at the workshop, by letter or email, immediately after the workshops and 1 month before follow-up

 (b) Research staff were asked to remind control workshop participants about their allocated workshop after the introductory talk, as well as 1 month and 1 week before the workshop

 (c) Research staff were asked to strengthen questionnaire-chasing letters

 (d) Research staff were also asked to follow-up experimental participants by telephone, letter or email who had not attended their allocated workshop

 (e) Research staff were asked to follow-up controls by telephone, letter or email any time after the 3-month period, as these participants could attend any control workshop that was being run

 (f) A script for following-up participants was developed which was more focused

 (g) A set of procedures was developed for following up participants, which included:

  (i) a pack of outcome assessment forms and letters

  (ii) a schedule for five instances of telephone contact with the participant

  (iii) if this failed, a shortened data assessment pack (by email or post)