Skov‐Ettrup 2014.

Methods	Country: Denmark Setting: online, participants were members of Xhale.dk Study design: RCT
Participants	Participants: 2030 (I = 1055, C = 975) daily smokers, 59.3% female Age range: 15‐25 years, mean (SD): I = 19.4 (3.1), C = 19.5 (3.2) Criteria for inclusion: daily smoker, aged 15‐25 years, valid email address or mobile phone number, self‐chosen quit date between 14 February 2007 and 1 August 2009 Follow‐up method: contacted via email to complete internet‐based questionnaire, email/text reminders sent after 4 days and after 11 days. If there was still no response after 18 days up to 4 attempts were made to contact participants over telephone Inducements to enter study: none Baseline characteristic equivalence: “At baseline there were no statistically significant differences between groups” Pre‐test smoking status assessment: self‐report, mean (SD) cpd: I = 15.4 (7.0), C = 15.6 (6.8) Post‐test smoking status assessment: self‐report
Interventions	Intervention: access to programme website, which included smoking facts, tests, exercises, videos and a chat forum. In addition there was the option of receiving tailored text messages. This entailed a weekly message up to 4 weeks before their quit date, and a daily message 1–3 days before the quit date. Then they received 2 tailored text messages/d during a period of 4 weeks. For the following 4 weeks, the frequency of text messages declined to 4‐5 text messages/week. The system generated 3 types of tailored messages based on 3 different tailoring parameters: self‐efficacy, beliefs about smoking and themes chosen by the user. Theoretical basis for intervention: Stage of Change theory and theory of planned behaviour Control: also had access to website and the option to activate text messages. These messages were less frequent and untailored. Messages were sent once daily for 5 weeks beginning 5 days before the chosen quit date. Weekly messages were sent for the following 3 weeks.
Outcomes	Measurement: 30‐day PPA Relevant follow‐up periods: 12 months Verification: none Loss to follow‐up: I = 73.7%, C = 71.9%
Notes	New for 2017 update. This review used all randomized participants, whether or not they chose to activate text messages.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Abstract states participants were "consecutively randomized", the meaning of which is unclear. No further details of the randomization process were present.
Allocation concealment (selection bias)	Unclear risk	Same problems as random sequence generation (above)
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants were unaware of the random allocation. Personnel did not deliver the intervention, as it was through text messaging and email.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	The majority of follow‐up took place online (although if participants did not respond to online prompts, interviews took place via telephone ‐ unclear whether assessors were blinded)
Incomplete outcome data (attrition bias) All outcomes	High risk	High rates of dropout as would be expected from online intervention however rates above 50%, 73.7% in intervention group and 71.9% in control group
Other bias	High risk	Participants were given the option to receive text messages so not all participants benefited from differential treatment between study arms.