The study was approved by the University of Auckland Human Participants Ethics Committee (UAHPEC, Ref 019659), and the study protocol has been published elsewhere [2]. Briefly, eligible parents or caregivers (hereafter referred to as parents) were randomly allocated to the MyTeen intervention program or care-as-usual condition. Data were obtained from all participants at baseline and at 1 month (end of intervention phase) and 3 months postrandomization. The trial is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12618000117213).

We aimed to recruit a representative sample of 214 parents (n=107 per randomized group; 1 parent per household) residing in New Zealand across a 6-month period. This sample size provided 80% power (P=.05) to detect a group difference of 2.5 (SD 5.8) in the primary outcome measure of Parenting Sense of Competence scale (PSOC) score at the 1-month follow-up and allowing for an estimated 20% loss to follow-up. The majority of the New Zealand population is of European descent (70%), followed by indigenous Māori (16.5%), Asian (15.3%), and Pacific (9%) descent [17]. Effort was made to oversample ethnic subgroups in order to allow for subgroup analyses. Parents were eligible for inclusion in the study if they (1) had a child aged between 10 and 15 years, (2) had access to a mobile phone, (3) were not receiving any professional assistance for their own and/or child’s mental health problems, (4) possessed adequate knowledge of the English language, and (5) provided informed consent. Only 1 parent from each household was recruited for the study. Parents who showed high level of stress, as reported by the Parental Stress Index (ie, score ≥72), were excluded from the study and directed to professional services. Interested individuals completed a phone screening to assess eligibility criteria and provide contact information. Eligible individuals were sent an email through which they provided informed consent and completed a baseline survey.

Strategies for successful recruitment and retention were considered at the onset of the project, and a recruitment plan was developed, monitored, and modified as needed throughout the project. Potential barriers (eg, budget constraints, timeframe, and attrition) and strategies to facilitate recruitment (eg, program content and recruitment material, staff characteristics, recruitment strategies, and study procedures) were identified. Each of these strategies are outlined below.

Care was taken to minimize participant burden, a factor that likely contributes to study enrolment and retention [19], to engage participants throughout the trial, and to maximize retention. Specifically, we anticipated that the delivery of the program via text messages would be a possible way to minimize participant burden by reducing logistic barriers for parents. Efforts were made to ensure that data collection at each time point was brief and took no longer than 10 minutes for participants to complete. Overall, each participant needed to spend only 1 hour (including providing study information, screening, baseline, and 1- and 3-month follow-ups), across a 3-month period, to complete the study, over and above the time to receive the program.

Screening and eligibility of interested participants were assessed over the phone. Our research assistant provided information about the study and made sure that the participants understood the importance of follow-up data collection being essential and integral to the research. Participants were explicitly told that participation involves completion of 3 sets of questionnaires at various time points. Eligible individuals had 2 weeks to provide consent and complete the baseline assessment. Personalized reminder emails were sent to eligible individuals between 3 and 5 days postscreening if they had not completed the assessment. On day 10, a phone call was made to remind the study participants to complete the baseline assessment. Up to 3 emails and 2 phone calls were made before the eligible participant was deemed unable to contact or as someone who refused participation.

Assessments were conducted immediately post intervention (1 month) and 3 months after randomization. To maximize data retention at each assessment, multiple methods of communications were used to support participant retention, including texting, emailing, and phone calls. Five days before the assessment was due, participants were sent a reminder email to thank them for their participation and remind them about the upcoming assessment. For the control group, the email also specified that the participant would have the option to receive MyTeen text messages upon completion of the final assessment. For participants who did not complete the assessment within 3 days of the assessment email, up to 2 text message reminders (3-4 days apart) were sent and a final email or phone call was sent after 2 weeks of noncompletion. We incentivized participants with a NZ $20 (US $13.60) supermarket voucher upon completion of all assessments and the option to be included in a draw for a supermarket voucher valued at NZ $150 (US $102).

Figure 1 shows the number of participants who expressed interest over time. We were unable to quantify successful enrolment for each strategy separately as they were not independent. Recruitment was tracked by the project manager (AW) and reported to the research team weekly. For the first 4 weeks, most of the recruitment effort focused on targeted minority recruitment. However, recruitment was slow, and only 22 individuals expressed interest, excluding those who expressed interest from the focus groups conducted during the development stage of the project (n=15). The research team therefore targeted the wider community and distributed advertising material through email lists and social media over the next 6 weeks, resulting in a surge in interest (n=93). By week 12, a total of 200 individuals had expressed interest, and our research assistants were at full capacity to screen all potential participants. Decision was therefore made to put recruitment on hold and resumed in week 16. After reviewing the demographic profile of all participants, a paid Facebook ad targeting ethnic minority groups was posted. A number of schools were also contacted for recruitment to increase the chance of recruiting minority groups. Over 22 weeks, 319 parents expressed interest in the study, at which point, all recruitment activities were ceased. Screening was conducted over the phone with all interested individuals; 50 (15.7%) participants were no longer contactable, 18 (5.6%) participants were no longer interested, and 15 (4.7%) participants were deemed ineligible prior to completing the screening process. In total, 236 (74%) participants completed screening, of which 48 (20.3%) reported hearing about the study via email; 64 (27.1%), via advertisements (websites); 64 (27.1%), via Facebook; 29 (12.3%), via referral, including word of mouth and face-to-face approaches; and 31 (13.1%), via other means (eg, schools). No specific strategy appeared to be more engaging for Māori and Pacific participants, which is likely due to the small sample of ethnic minorities. Similarly, due to the small sample of fathers, no difference was observed among different recruitment strategies. Data on demographics were obtained at baseline.

Table 2 presents the demographic characteristics of the study sample. The final sample resulted in 221 randomized participants who met the eligibility criteria, exceeding our recruitment target of 214 participants. The sample comprised 210 (95%) mothers (including stepmothers), with a majority (167/221, 75.6%) of participants identifying themselves as European, followed by Māori (29/221, 13.1%), Pacific (17/221, 7.7%) and other (8/221, 3.6%).

Attrition was low at the 1-month (4.5% overall; intervention group: n=5, 4.6%; control group: n=5, 4.5%) and 3-month (9% overall; intervention group: n=10, 9.2%; control group: n=10, 8.9%) follow-ups. On average, participants in the intervention and control groups took 3.72 (SD 5.43) and 2.33 (SD 3.83) days, respectively, to complete the 1-month assessment, and 3.82 (SD 6.74) and 4.09 (SD 7.71) days, respectively, to complete the 3-month assessment.

First, reliance on traditional recruitment methods, such as distribution of flyers and posters, targeted minority recruitment via word of mouth, and community referral was not particularly effective. There were few referrals from community organizations where we had posted our flyers. Similarly, handing out flyers at community events resulted in limited responses. It is likely that merely posting and handing out these flyers was not enough in these settings. Recruitment of parents from schools attended by their children was also not very fruitful. In all, 388 schools nationwide were contacted for recruitment, but only a few responded. Nonetheless, those that did advertise our study spiked an increase in expression of interest. Our findings on engagement with schools are similar to that of other studies [20]. A previous study that recruited parents of primary school students into a smoking cessation trial reported similar challenges, wherein only 16.3% of the schools contacted agreed to distribute recruitment materials [20]. Although schools can be a valuable resource for recruitment, gaining access to schools proved to be very challenging and time consuming. Studies that have successfully worked with schools to recruit participants (usually students) suggest that it requires extensive planning (ie, fitting the timeframe of the school terms), building relationship with the school, connecting with key contacts, and contributing to the best interest of schools [21]. This may not be feasible for studies that are resource constrained.

Web-based strategies appear to have yielded the most response in our trial. A number of parents responded to our Facebook post and website advertisements. The use of email listserv also appeared to have yielded a spike in interest; however, it was not possible to know how many parents were reached, as individuals were encouraged to forward the email to others who might be interested in the study. It is worth noting that the ability of email lists to target a select population may result in a sample that is not representative of all parents. Our advertisement email sent to the University listserv resulted in sample of highly educated parents, which was thus less representative of the general population. Obtaining permission to post to listservs, which may accept posts only from group members, can also be challenging. Nonetheless, this approach required minimum staff effort. Studies examining web recruitment strategies have reported large variation in how many participants researchers can recruit, cost per participant, diversity of the sample, and the length of time required for recruitment [4,22]. This has implications for researchers and areas of study that may not have the funding required to enable large-scale recruitment using more traditional recruitment methods [4].

Second, although we actively sought to recruit ethnic minorities, we failed to attract interest. We were aware of our limitations at the onset of the project in recruiting minority populations but were restricted by resources and time to address the challenges. We recognize that recruitment strategies should be culturally sensitive and tailored to the needs of a given group. Time to build relationships and resources to comprehensively reach a community is a requisite. By developing a partnership with trusted individuals and organizations early during the research process, researchers can build a bridge to communities that may feel disenfranchised from traditional academic research [7,23,24]. Although these strategies are intensive and expensive to build and sustain [24], they are essential if the experience of these groups with interventions is to be evaluated.

In addition to the strategies used, the success of our recruitment and retention efforts may have been attributed to the following factors. First, careful planning and continuous monitoring throughout the recruitment process appeared to be critical for success. We set realistic recruitment targets, monitored progress, and modified our recruitment plan against those targets as needed. Recruitment was boosted when there was a decline in interest, whereas recruitment strategies were put on hold when there was a sudden increase in the expression of interest, leading to a backlog of participants requiring to be screened. A high degree of flexibility in the recruitment strategies was thus deemed necessary.

Second, our use of simple appreciation and reminder emails between assessments appeared to help with participant retention. On average, participants completed the follow-up assessment within 2 to 3 days of receiving the email link to the survey. These efforts encouraged participants to feel connected to the project, fostering an overall sense of commitment from the beginning through the completion of the study.

Third, the strength-based and delivery mode of the program may have attributed to achieving our target sample. The framing of the program as a strengthening approach to support families was important. This led to subsequent communication with potential participants in a positive way and reduced the stigma of help-seeking. For example, our formative work identified that the word “intervention” was off-putting for parents; hence, the word “program” was used in all subsequent advertising material for the trial. In addition, text messaging was a proactive approach to delivering parenting information to participants, requiring minimal effort and time commitment. The low attrition rate in our study is consistent with other studies on text messaging programs. Previous meta-analyses across a variety of text messaging–based programs found a mean retention rate of 86% [25], with retention rates ranging from 46% to 96% [26]. In our study, the ease of access is likely to have increased participation, as time constraints and logistical barriers are often raised by parents as barriers to continuation in parenting programs [27]. There has been growing acknowledgement in parenting program research for different modalities, including web-based alternatives and mHealth technology [12,28]. Our trial demonstrated the feasibility and effectiveness of providing brief preventative parenting support solely via text messages.

Finally, there was a demand for support for parents of adolescents in New Zealand. Our formative work reported that parents perceived a lack of support in the community and were interested in parenting support [18]. Many parents identified everyday parenting challenges and were interested in learning about positive parenting strategies, adolescent development, tips for improving parent-adolescent communication, and evidence-based resources. The findings were reinstated in our main trial, where parents expressed the need for more information and reported high satisfaction with the program [10].

Our target population comprised parents of New Zealand adolescents. Therefore, the findings may not be generalizable to studies involving other populations. Different recruitment strategies also vary substantially in cost per participant recruited, but because the study was not designed to compare the effectiveness or cost-effectiveness of recruitment strategies, we are unable to estimate the cost-effectiveness and the investment yield ratio for these strategies. Rather, our findings provide lessons to inform future studies.

Despite efforts to recruit parents from diverse population groups, our sample was predominately female, married, and of high social economic status. Many of our participants have also completed tertiary education. This is consistent with past research that reported higher levels of parent education is a predictor of parent uptake in programs [7].

Fathers were underrepresented in our study. This is a common challenge in parenting research, with fathers considered as hard-to-reach parents [29]. A meta-analysis of the parenting program Triple P found that of 4959 participants in 21 studies conducted across several countries, only 20% were fathers [30]. Underrepresentation of fathers as participants in parenting programs is concerning. Qualitative studies conducted with fathers of young children found that many fathers perceived parenting programs to be designed for mothers and that they were reluctant to seek parenting support from any formal source, as help-seeking was perceived by men as a failure and conflicted with their views on masculinity [31]. Advertising efforts that are not directed at fathers, are not related to them, or are perceived as stigmatizing are unlikely to reach fathers. Other barriers included services deemed as untrustworthy, uninterested in, or even hostile toward fathers [32,33]. Overcoming the above barriers are important to successfully engage fathers in such research. Research to understand how their engagement and participation can be maximized is urgently needed.

We also did not obtain any information from those who did not participate. Parents who do not initially engage could reveal different barriers or characteristics to those recruited into the program. Their views are therefore important and should be captured in future studies.

Recruitment and retention are critical aspects of research for parenting programs, and it is unlikely that there will be a one-size-fits-all recommendation. It is therefore important that efforts are well documented to enable researchers to make more informed decisions on how and where to best recruit and therefore maximize outcome [34].

With the rapid development of technology and web-based platforms, the field would greatly benefit from empirical research designed to test the efficacy and necessity of different recruitment and retention strategies, as well as more detailed reports regarding recruitment and retention methods. Web-based recruitment strategies provide a viable means for obtaining a geographically diverse sample. Recruiting the most affected populations should be a priority, and more resources are needed to do so. Further research is needed to examine the effectiveness of tailoring recruitment strategies to different populations.