Randomisation and blinding
Allocation was done according to a computer-generated random sequence. Participants were stratified according to which of the two versions of the intervention was appropriate (general or surgery). Block randomisation was used to ensure equal number of participants in each group within stratum, using random block sizes of 2 and 4. Randomisation was done immediately after participants responded to the baseline questionnaire using their mobile phone. Once a response was received by the backend server, allocation took place automatically, and participants were told about group allocation via a text message. Research personnel were not able to affect the allocation and all study procedures were automated, preventing subversion of allocation concealment.Participants were aware of their group allocation; however, research personnel were blinded. All questionnaires were completed by participants on their own mobile phones, without supervision by research personnel. Non-responders were called, and during the call, it was possible that participants revealed their allocation to assessors. This means that there was a risk of detection bias (see Limitations).