Study to test the content of the most effective SMS reminder message to reduce missed appointments in hospital outpatient clinics

INTERVENTION: The study involves 10,000 patients at clinics at Barts Hospital who have agreed to receive text message reminders about their appointment. Patients are allocated to receive one of four different messages at random (randomised using the Mersenne twister method). The messages are as follows: Control: ?Appt at on at . To cancel or rearrange call the number on your appointment letter.? We propose to retain this current SMS message as a control while introducing the following variants Trial arm A: ?Appt at on at . To cancel or rearrange call 0207389471.? Reducing even apparently minor barriers to carrying out a behaviour can significantly increase the incidence of that behaviour. For example, a seminal study from the field of social psychology found that vaccination uptake was low even after education had been provided and broad intentions formed. However, uptake increased from 3% to 28% by simply providing a map and asking participants to think about an appointment time: these small 'channel factors' made a large difference (Leventhal, Singer, and Jones, 1965). Similarly, it is likely that the process of having to locate the appointment letter reduces the effectiveness of the control message. We have been advised that it is possible to include the specific telephone number, and we would like to test the impact of doing so: Trial arm B: ?We are expecting you at on at . Nine out of ten people attend. Please call 0207389471 if you need to cancel or rearrange.? There is much evidence that even short messages based on social norms ? saying what other people do in the same situation ‐ can have a significant effect on compliance (e.g. Hallsworth et al., 2013). Given that only around 10% of patients do not attend, there is a clear opportunity to leverage social norms: Trial arm C: ?We are expecting you at on at . Not attending costs NHS £160 on average, so call 0207389471 if you n CONDITION: N/A ; Not Applicable PRIMARY OUTCOME: Number of patients who attend their outpatient appointment INCLUSION CRITERIA: All patients over the age of 18 at five clinics at Barts Hospital who have already provided their mobile phone number to Barts Hospital, for the duration of the trial