From the PubMed abstract: "A randomized controlled trial investigated the impact of SMS appointment reminders (two levels: present or absent) on client attendance (three levels: attended, rescheduled, or did not attend) and dropout (two levels: completed treatment or terminate early). Participants (N = 140) at an outpatient psychology clinic were randomly allocated to either receive an SMS appointment reminder one day before their scheduled appointment, or to receive no reminder."