Table 2.

Text message characteristics that merit consideration during the design phase.

Text message characteristic	Features	Features adapted in TEXT ME and TEXTMEDS studies
Message customization	The message content can be generic or individualized	Both studies sent messages with content that was partly generic and partly customized to participant’s needs eg, smoking status, diet (vegetarian or nonvegetarian) and types of medications.
	Ability to update custom settings. (particularly relevant for a long-duration study).	TEXT ME: Customization was only at baseline. TEXTMEDS: Allowed flexibility to changes in participant’s status such as behaviors or medication eg, if a participant successfully quit smoking and requested to stop smoking-related messages, this could be honored anytime during the 12-month study.
	Simple versus complex customization	TEXT ME: Relatively simple algorithms using minimal baseline data. TEXTMEDS: More complex customization using baseline data, and the ability to modify during the course of the program.
Personalization	This may enhance participant’s engagement with the program	Both studies implemented this function.
Delivery timing	Needs to consider intrusiveness of messages delivered during working hours, out off hours, weekends, and public holidays	Both studies sent messages on working days during working hours. Occasional season’s greetings message on holidays.
	Random times may prevent habituation.	Both studies implemented random delivery times on random weekdays.
	Specific times—delivery timed with a specific behavior eg, medication intake	We did not implement this aspect, as network latency times cannot be measured with confidence.
Frequency	Number of messages per day or per week	Both studies sent 1 message per day, average 4 messages per week.
	Fixed versus variable frequency	TEXT ME: A consistent schedule of 4 messages per week on random weekdays. TEXTMEDS: The frequency of messages varied from 2-4 per week on random weekdays.
Order of message content	Structured delivery may increase participant interest in program eg, patients hospitalized for myocardial infarction—early messages can focus on recovery and tips like use of prn nitrates; later messages can focus on healthy lifestyle, medium, and long-term goals	TEXT ME: Messages were written to stand on their own and not rely on previous messages. Hence, could be delivered in a random order. TEXTMEDS: Messages were delivered in order, enabling the ability to deliver a structured story. Messages delivered may reference a previous message. Participants received messages according to protocol-driven timing ie, on a given day each participant received a unique message, which may be different from other participants, but was appropriate to their duration on the study.
Unique messaging and repetition	Nonrepetitive messages, repetition of key messages or repetition of key message after rewording	TEXT ME had nonrepetitive messages TEXTMEDS had some repetitive key messages.
Two-way interaction	May increase patient engagement	TEXT ME was a one-way study. TEXTMEDS was two-way study. Participant replies were methodically logged and actioned by the health counselor.
Character set	Non-Latin (Unicode) characters are better avoided; alternatively, they must be tested for correct transmission by network operator and decoding by the recipient’s mobile phone	Both the studies had the capacity to support Unicode but did not implement this.
Readability	Avoidance of medical jargon and abbreviations	Both studies considered 5th-8th–grade reading level [15]. Text messages were pilot tested among prospective patients who were specifically asked about readability.
Message length	Preferred length ≤160 characters (including spaces)	In both studies the messages had a character count that ranged from 120-160. Longer messages are often delivered fractionated; consequentially may result in increased message send cost and unintelligible formatting by recipient’s handset.
Sender signature	Helps source recognition and distinguish the messages from spam. May be mandatory, refer to country-specific legislation	In both studies, participants were encouraged to save the study mobile number in the “contacts directory” of their mobile handsets. A full signature was included in the first message. Subsequent messages used abbreviated signature due to 160 character limit per text messages.
Unsubscription	Clear instructions for unsubscription; keyword - “STOP” or “OPT OUT” or “Unsubscribe”	Both studies included unsubscribe information with the first message. It was not possible to send unsubscribe information to participants with each message due length exceeding 160 characters. Legal advice recommended a way to consent participants so that this was not required.