The study was a two-arm, 12-month, randomized controlled, Internet-based trial with continuous recruitment and data collection. The allocation ratio was 1:1. The intervention arm in the trial received tailored messages in addition to the basic functionality of the Internet-based intervention for smoking cessation, while the control arm did not. Enrollment started on August 15, 2006 and ended December 7, 2007. The study was approved by the Regional Ethics Committee for North Norway (REK-NORD) and the Norwegian Privacy Ombudsman for Research. The randomized controlled trial was initiated before trial registration became customary in Norway, and therefore does not have a trial identification number.

The Intervention website was announced as a new and free service to aid in smoking cessation in the local and national media. All participants agreeing to the informed consent form were subsequently automatically allocated through use of an online random number generator to the intervention or control arm (for the informed consent form, see Multimedia Appendix 1). Altogether 3054 visitors registered to use the Norwegian website slutta.no. The front page displayed the logos of the Norwegian Directorate of Health’s Quitline, the Norwegian Cancer Society, and the Norwegian Centre for Telemedicine (for a screenshot of the front page of the intervention, see Multimedia Appendix 2). Registration required providing a unique email address, so potentially, using several email addresses, a person could have registered more than once. Among registrants, 30 were excluded (20 because they were under age 16 years and 10 because of missing group allocation). Another 726 registrants had already quit smoking and were excluded from the current analyses. Among the 2298 participants who smoked at enrollment, 1029 were randomly assigned to the intervention and 1043 to the control arm (Figure 1).

The participants filled in an extensive questionnaire at the time of enrollment. This included information on such demographic variables as gender, age, education, and work situation. The participants also provided a quit date and an email address. Further, they completed a smoking-cessation maintenance self-efficacy questionnaire, reported on smoking behavior, and stated their motivation for cessation. The tailored messages were created on the basis of these questionnaires and were sent to the intervention group on their personal webpage and by email (for a screenshot of My Page, see Multimedia Appendix 2). Participants in the control group did not get any messages on their webpage and only emails containing notifications and reminders for the follow-up questionnaires.

Both arms received an email message with a link to a questionnaire on self-efficacy and smoking behavior at 1, 3, and 12 months after the date of enrollment. On completion of the questionnaire, the participants could enter a draw to win prizes such as books and T-shirts. Nonresponders received up to three reminders.

The intervention consisted of multiple intervention components and was intended for long-term follow-up. The website included static information on the dangers of smoking, general advice on smoking cessation, and information about the website. In addition there were interactive tests for nicotine addiction, type of smoker (stress smoker, comfort smoker, etc), and motivation level.

There was an emphasis on creating opportunities for social interaction using a discussion forum, a guestbook, and a personal diary (Multimedia Appendix 3). The participants could invite friends and other participants to support them by leaving messages in the guestbook, and to publish their own smoking-cessation diary. There were also some community features: participants could click on other participants’ nicknames in the forum and thereby get a specific profile with some information about the other participant, for example. The possibilities to interact were only as described above, as there were no opportunities for synchronous communication through chat or private messaging between the participants.

During the 12-month intervention, the participants in the intervention group received up to 150 tailored messages. The first message was sent 14 days before, and the last, 12 months after, the quit date. The frequency of the messages varied over the course of the 12 months, as they were sent out on a defined number of days before or after the quit date. In the beginning messages were sent daily, then the frequency was decreasing slowly during the first 3 months with a substantial drop-off 3 months after the quit date.

The tailoring was set up on the basis of several different types of variables. Personalization-, adaption-, and feedback-type tailoring were all used to varying degrees. Table 1 lists examples of variables for tailoring. The self-efficacy messages were more specifically about confidence in refraining from relapsing in different situations, also known as maintenance self-efficacy [7]. In concordance with several stage and process models of health behavioral change, such as the Health Action Process Approach [7], we aimed at providing these as preparation to transition from conscious behavioral change (action) to lifestyle integration (maintenance). In this intervention we did not assess where participants were in their process through a questionnaire, but we did send maintenance self-efficacy messages to those with a low maintenance self-efficacy at 3 months past their quit date. There was no other tailoring based on a health psychological stage or process approach in the current intervention. Besides the messages concerning addiction, the rest concerning benefits of quitting smoking, social support, etc, were evenly distributed over the year, with decreasing frequency.

The tailored messages could also be retrieved from a calendar on the participant’s My Page. Other tailoring features on this page included a personalized greeting, feedback on number of smoke-free days and the amount of money saved, and a list of the reasons the participant had entered for wanting to quit smoking.

Data were gathered on age, gender, education, perceived tailoring, perceived usefulness of the website, self-efficacy, and smoking. Education was rated on a 5-point scale: 1, ≤9 years of total education; 2, 10–11 years; 3, 12 years; 4, 13–16 years; and 5, ≥17 years. Motivation was assessed with a single question, “How strong is your motivation for quitting smoking?” The participant answered on a 4-point scale ranging from “very weak” to “very strong.” Previous research has found that a similar single-item measure for motivation had comparable predictive validity to a multi-item instrument [8].

Data on the use of the interventions were gathered through Web logging. The number of log-ins and time spent at the site (in minutes) per user were registered. At the 1-month follow-up, the participants were asked whether they would recommend the site to a friend and to rate from a list of intervention components the one that they found the most useful.

Smoking behavior was assessed at the baseline and at 1-, 3-, and 12-month follow-ups as 7-day abstinence rates through the question “Have you during the last 7 days had a smoke, even just a single puff?”

Data on smoking-cessation maintenance self-efficacy were gathered at baseline and after use of the site for 1 month and 3 months, using the 12-item Smoking Self-Efficacy Questionnaire [9,10]. The 12 items consist of 6 items addressing perceived ability to refrain from smoking in the face of internal stimuli such as when nervous, and another 6 items addressing external stimuli such as when with other smokers. The scale has previously been shown to predict smoking cessation, to be negatively related to number of cigarettes smoked, and to have the ability to discriminate between stages of change [10]. The same study [10] found that the internal consistency was alpha = .94 for the internal subscale and alpha = .89 for the external. At baseline the items were rated on a 5-point scale that was later recoded into a 6-point scale (2 = 2.25, 3 = 3.5, 4 = 4.75, 5 = 6, ELSE = Copy), and on a 6-point scale at 1- and 3-month follow-up (1 = not confident at all, to 6 = completely confident). This recoding was necessary because in the tailoring questionnaires, which provided the baseline data, we used the original 5-point response format of the SEQ-12 [9] while, for purposes of conformity of response format in the evaluation questionnaires, we used a 6-point scale here.

Perceived tailoring was assessed with 4 items from Dijkstra [3] evaluating to what extent the user feels that the information is adapted to his or her personal situation. Agreement with these 4 items was rated on a 6-point scale ranging from 1, completely disagree, to 6, totally agree.

We based our a priori sample size estimation on a paper by Strecher [11], pointing out that previous computer-based smoking-cessation intervention studies have found group differences in abstinence rates of about 2%. Using abstinence rates at 12 months that only slightly exceeded no intervention (6% and 8%) and a 1-sided test without continuity correction at a .05 alpha level and with 90% power, we needed a total sample of 2787. Also, we expected to have to raise the number of participants recruited further by 40%–60%, that is, to around 4000, because of the high dropout often observed in Internet-based interventions [12].

No items had more than 5% missing data at the baseline; we therefore assumed missing data to be missing completely at random. On the variables s elf-efficacy and p erceived tailoring, we replaced the missing data with values imputed by the expectation maximum likelihood algorithm in SPSS version 16.0 (IBM Corporation, Somers, NY, USA) before analysis of variance. Internal consistency was measured by Cronbach alpha. Nonresponse on 7-day abstinence was dealt with by counting all participants with missing data as smokers (ITT). We compared the ITT quit rates with the quit rates for responders only.

Differences in dichotomous baseline characteristics and in abstinence rates between groups at all time points were analyzed with a regular chi-square test. Group differences in continuous variables were analyzed with t test. The Mann-Whitney U test was used for comparing the usage of the intervention between groups, as these distributions were nonnormal. Effect sizes for group differences at the different time points were calculated as relative risk.

Mediation was tested using an approach developed by Preacher and Hayes [13] using their SPSS macro [14]. Bootstrapping (5000 samples) with bias correction and acceleration was used to create a 95% CI around the point estimate of the indirect effect, with an interval not including zero indicating a significant indirect effect.

Both recruitment and data collection were continuous, and were maintained right until the point of data extraction. This implies that at the time of data extraction, some users of the intervention had been followed up for a few days and others for the full 12 months. In Figure 1 those participants not having had the possibility to reach the next follow-up time point are indicated as “Not yet reached follow-up time point,” while the true nonresponders are indicated by “Nonresponse”. The overall response rate was 36.8% (728/1981) after 1 month, 28.1% (506/1798) after 3 months, and 28.8% (244/847) after 12 months. There were no significant differences in response rates between the two groups at any time point (1 month: χ² ₁ = 0.58, P = .45; 3 months: χ² ₁ < 0.001, P = .99; 12 months: χ² ₁ = 0.51, P = .48).

Overall among the participants, 72.26% (1497/2072) were female, mean age was 37 years, 17.1% (353/2072) had 17 or more years of education, mean motivation score was 3 (range 1–4), mean self-efficacy score was 34 (range 0–60), mean number of cigarettes smoked per day was 16.

As can be seen in Table 2, there were no significant differences between the intervention and the control group at baseline. Furthermore, no group differences in demographics were found at the follow-up time points.

Table 3 displays the time spent on different activities at the website according to study arm. The intervention group had logged on more times ( P = .03) and had used the site more overall ( P = .02). In more detail, the intervention group had used My Page more ( P = .03) than the control group had. The most used component of the intervention was the discussion forum, followed by My Page, while the Facts section was used much less. More detailed analyses on the use of the intervention over time can be found in Wangberg et al [15].

In the intervention group, 88.4% (320/362, 95% CI, 84.7–91.3) of the users stated that they would recommend the site to a friend, compared with 71.8% (255/355, 95% CI, 66.9–76.3, P < .001) in the control group. Further, in the intervention group, 34.0% (123/362, 95% CI, 29.3–39.0) of the users ranked the tailored emails as the most useful intervention component, compared with 6% (21/355, 95% CI, 3.9–8.9, P < .001) in the control group (who did not receive any emails besides one with username and password upon registration and emails with links to follow-up questionnaires). In the intervention group, 10% (37/362, 95% CI, 7.5–13.8) of the users ranked general information as the most useful component, compared with 22% (79/355, 95% CI, 18.2–26.9, P < .001) in the control group, while 15% (55/362, 95% CI, 11.9–19.3) of the users in the intervention group ranked the discussion forum as the most useful component, compared with 21% (73/355, 95% CI, 16.7–25.1, P = .06) in the control group. The remaining nominations were evenly spread over the 10 other functions the user could choose as the most useful.

The p erceived tailoring scale was found to have good internal consistency at 1-month (alpha = .92) and 3-month (alpha = .94) follow-up. Table 4 shows mean scores on perceived tailoring by group at 1- and 3-month follow-ups. The intervention group had higher perceived tailoring scores at both time points (Ps < .001).

Table 5 shows that the ITT 7-day abstinence rate at 1 month was 15.2% (149/982) among those receiving the tailored intervention, compared with 9% (94/999) among those who did not (P < .001). The corresponding figures at 3 months were 13.5% (122/902) and 9% (84/896, P =.006) and at 12 months were 11% (47/419) and 12% (50/428, P = .91). The same group differences were found looking at responders only (Table 5).

Both the internal (alpha = .93) and the external (alpha = .86) self-efficacy subscales were found to have good internal consistency at 1-month follow-up. Table 6 shows the mean scores for self-efficacy at all follow-up time points. Self-efficacy was higher for the intervention group at 1- (P = .01) and 3-month (P = .002) follow-ups, but not after 1 year (P = .58), paralleling the results for the main outcome.

We performed a mediational analysis (n = 386) with group as the independent variable, 7-day abstinence at 3 months as the dependent variable, and self-efficacy and perceived tailoring at 1 month as the proposed mediators. The total effect of group on abstinence rates at 3-month follow-up was 0.66 (Wald χ² ₁ = 9.82, P = .002). Self-efficacy accounted for an indirect effect of 0.33 (95% CI, 0.08–0.60), while perceived tailoring did not have a significant indirect effect (point estimate = 0.003, 95% CI, –0.09 to 0.10). The remaining direct effect of group on abstinence rates was 0.58 (Wald χ² ₁ = 5.82, P = .02).

This randomized controlled trial found that tailoring an Internet-based intervention for smoking cessation increases success rates in the short term, but not in the long term.