Mobile health (mHealth) is transforming health delivery as a highly convenient and effective approach for supporting individuals with chronic conditions [1-3]. Delivered via phones, tablets, and wearables, mHealth provides education, motivation, monitoring, and other forms of support to improve health behaviors. SMS text messaging is one form of mHealth that is uniquely poised to benefit everyone, including people who are older, are disadvantaged, and are from traditionally minoritized racial or ethnic backgrounds [4-6]. A critical factor influencing mHealth effectiveness is users’ engagement or interaction with the technology, which is typically measured via system use [7-9]. Across the mHealth literature, engagement tends to be highly variable [10,11], which has spurred a whole body of research that aims to understand predictors of engagement, including user characteristics and intervention features (eg, intervention duration and frequency of sending content) [10-14]. However, very little research has attended to the type of mHealth content that users are expected to engage with [15] and, more specifically, how the content may be requesting more or less cognitive reflection.

The primary goal in having users engage with mHealth content is health behavior change. With respect to mHealth interventions, there is a hyperfocus on wanting the user to interact with the technology (eg, responding to a text message), with less consideration of whether the user is reflecting on the content cognitively (eg, reflecting on past behavior and planning future behavior) [8]. Although interaction with the technology is a critical measure, there is a growing consensus that cognitive investment is also important for meaningful behavior change in many types of mHealth interventions [16-18]. Notably, content may be designed in a way that represents a low response burden, thereby easily eliciting a response (ie, producing high engagement), but such content may not evoke the necessary cognitive reflection required to change behavior [18]. Alternatively, content that is designed to encourage deeper reflection may overwhelm users, which risks them disengaging completely. Understanding how to strike the balance between response and reflection has critical implications for effective engagement (ie, engagement needed to impact outcomes) [19]. To our knowledge, no studies have explored the association between reflection demands and the degree of interaction with an mHealth tool. Understanding the interplay between reflection burden and response burden will help guide the design of interventions seeking to strike this balance.

Our team previously developed an mHealth intervention (delivered via text messages and phone calls) called Family/Friend Activation to Motivate Self-care (FAMS) [20,21]. FAMS is a diabetes self-management intervention that targets persons with type 2 diabetes and provides the option for persons with diabetes to invite a support person to also receive text messages. We recently evaluated FAMS in a randomized controlled trial (RCT) [22], and during routine monitoring in the first few weeks of the trial, we observed a low response rate to text messages among support persons. Because support persons’ engagement with the text messages was an optional component of the intervention, we determined that this was an opportunity to explore how changing the content of these texts might impact response rates without compromising our ability to evaluate FAMS’ effects. Over the course of the RCT [22], we used a pragmatic approach to vary both the reflection burden and the response burden of the two-way text messages sent to support persons assigned to the intervention. In this observational study, our primary goal was to explore how these variations would impact users’ engagement with text messages, as measured via response rates. We also explored support persons’ characteristics that were associated with response rates for each type of text and described the different responses to each text.

This study was conducted as part of the FAMS 2.0 RCT. The trial design, intervention details, and outcomes for persons with diabetes and support persons were published [22-24]. For the trial, dyads comprising a person with diabetes and their support person were randomized to FAMS or a control condition. We recruited persons with diabetes who were receiving care for type 2 diabetes at Vanderbilt University Medical Center primary care clinics. Enrolling persons with diabetes were asked to invite a support person to participate with them and receive text messages; however, support person invitation and enrollment were not required. We defined a support person as any family member or friend with whom the person with diabetes would feel comfortable talking about diabetes management and health goals. Eligible support persons were aged ≥18 years, could speak and read English, and had a mobile phone separate from that of the person with diabetes. The only exclusion criterion was the inability to receive and respond to a text after training. For this study, we analyzed data from support persons in dyads that were randomly assigned to the intervention group (FAMS).

The Vanderbilt University Institutional Review Board approved all study procedures (institutional review board number: 200398; approved April 8, 2020), and the trial was registered on ClinicalTrials.gov (trial number: NCT04347291).

Persons with diabetes received daily text message support and monthly coaching sessions, during which they set behavioral diabetes self-management goals (as detailed by Mayberry et al [22]). Support persons received text messages that were designed to increase dialogue about and facilitate their involvement in the diabetes self-management of the persons with diabetes; a one-way message was sent 3 to 4 times per week, and a two-way message (also known as an interactive text message) was sent once per week. One-way messages were either a general text message about providing diabetes self-management support or a text message tailored to the identified diabetes goals of the persons with diabetes. Two-way messages asked support persons about how they supported the health of the persons with diabetes. Support persons who replied to the two-way text received an automated response, thanking them for their answer.

Although an individual support person’s intervention experience lasted 9 months (36 wk), intervention delivery for the trial lasted 2 years. Over the course of those 2 years, we varied both the response burden (the level of information requested for the response relative to that of other messages) and the reflection burden (the level of cognitive reflection requested relative to that of other messages) of the weekly two-way text messages, which were sent to support persons in 6 fixed periods (ie, waves). The waves coincided with the weeks of the trial; they did not coincide with the weeks of each individual support person’s intervention experience. Figure 1 includes the content for each version of the text message, the weeks of the trial when each text was sent (ie, calendar time), and the respective waves. We started the trial (wave 1) by sending a text message that was high in both reflection burden and response burden (high/high). In wave 2, we tested a text that was low in both reflection burden and response burden (low/low), and then in wave 3, we tested a text that involved medium reflection burden and low response burden (medium/low). In wave 4, we retested the high/high message to help determine if the point at which the text was sent during the trial impacted engagement. In wave 5, we sought to delineate the relative impacts of reflection burden and response burden; therefore, we tested a text message that was high in reflection burden and low in response burden (high/low). Finally, we closed out the trial by retesting the low/low text message (wave 6). The decisions about what messages to test were made iteratively based on response rates to the prior message, with the goal of learning how much reflection we could request while still achieving a relatively high response rate.

Of note, each support person only received the versions of the two-way text message that were sent during their 36-week trial participation, with most (120/148, 81.1%) receiving 2 or 3 different versions and no participants receiving the same message in 2 separate waves. Because this analysis used data from support persons only, we refer to them as participants henceforth.

In the trial, of the 150 support person participants who were enrolled and randomized to receive the FAMS intervention, 2 withdrew before the intervention started. The remaining 148 were included in the analyses (Table 1). The mean age was 50.3 (SD 14.7) years; 28.4% (42/148) of participants were men, and 33.1% (49/148) reported a minoritized racial or ethnic background. The mean length of education was 14.9 (SD 2.5) years, and 31.1% (46/148) of participants had annual household incomes of <US $50,000. Over half (84/148, 56.8%) were spouses or partners of the persons with diabetes, and 70.3% (104/148) were cohabitating with the persons with diabetes. Further, 9 participants withdrew at some point during the intervention; the analyses below reflect their engagement during the time they participated.

Figure 2 presents the proportion of two-way text messages that received a response within each week of the trial (ie, by calendar time). Notably, text message response rates for waves 1 and 4 (both were high/high message waves) were comparable, as were those for waves 2 and 6 (both were low/low message waves). Table 2 includes descriptive statistics for the overall and participant-level response rates for each version of the two-way text. The median response rates for the high/high, medium/low, and low/low messages were 23% (IQR 0%-51%), 75% (IQR 38%-96%), and 90% (IQR 61%-100%), respectively. When we kept reflection burden high but lowered response burden in the high/low message, the median response rate (10%, IQR 0%-40%) was closest to that for the high/high message, suggesting that reflection burden was responsible for the lower response rates seen with the high/high message.

We also compared the odds of responding to the four versions of the text message (Table 3). When compared to the high/high message, the odds of responding to the low/low message was 53% (95% CI 42%-65%) higher, the odds of responding to the medium/low message was 40% (95% CI 31%-49%) higher, and the odds of responding to the high/low message was 7.5% (95% CI 0.7%-14%) lower. All other pairwise comparisons (Table 3) indicated decreasing odds of responding at increasing levels of reflection burden.

Table 4 presents estimated incident rate ratios, along with 95% CIs and P values, from multivariate Poisson regression models that were used to identify participant characteristics predictive of response rate. Younger participants, participants who were not cohabitating with the persons with diabetes, and participants who had a lower socioeconomic status had lower response rates to both the high/high message and the medium/low message compared to those of older participants, participants who were cohabitating, or participants who had a higher socioeconomic status, respectively. The only characteristic associated with response rates for the low/low message was gender, such that men had lower response rates. Further, the only characteristic associated with response rates for the high/low message was age, such that younger age was associated with lower response rates. Across message versions, younger participants had lower response rates to any message with more burden than the low/low message, and participants who were not cohabitating with the persons with diabetes had lower response rates to the higher-burden messages than those of participants who were cohabitating. Race, ethnicity, health literacy, and baseline helpful involvement provided to the person with diabetes did not show patterns indicating the prediction of response rates to any message version.

In this section, we report on engagement at the text message level (vs the participant level). For the high/high messages, 1429 texts were sent, and 445 responses were received. Further, 13 responses were excluded from the analysis because the content was uninterpretable or was not relevant to the two-way text prompt. The reviewers categorized each response into the high- or low-effort response category, with 98.6% (responses: 426/432) agreement; of the 426 texts agreed upon, 350 (82.2%) were categorized as high-effort responses, and 76 (17.8%) were categorized as low-effort responses. For the low/low texts, 1791 texts were sent, and 1341 responses were received; almost all of the responses were “yes” responses (n=1239, 92.4%), while only 97 (7.2%) were “no” responses, and 5 (0.4%) were considered “other” responses. For the medium/low texts, 1847 texts were sent, and 1218 responses were received; the most common response was a “5” response (n=681, 55.9%), followed by a “4” response (n=338, 27.8%) and then a “3” response (n=144, 11.8%). Lastly, for the high/low texts, 446 texts were sent, and 109 responses were received; most of the responses received were “OK” responses, as requested in the message (n=86, 78.9%).

Despite the potential of mHealth to enhance self-management support and quality of life, there are still key gaps in understanding how to optimize mHealth engagement [16,17,19]. Most engagement research reports only on system use without consideration of the cognitive reflection done in the process of engaging with the content [16,29]. Ideally, we want to encourage reflection that results in meaningful behavior change, but it is unclear how much we can request, with respect to reflection, before users disengage. We varied the reflection and response burdens of two-way text messages to examine how these variations impacted users’ engagement, as assessed via response rates. We found, generally, that as the reflection burden of the message increased, participants’ engagement decreased. Importantly, when the same version of the text was sent at different points in the trial, participants’ engagement was consistent, suggesting that the message itself was key for response rates. The response rates for the high/low message were similar to those for the high/high message, and this supports reflection burden (vs response burden) being the primary driver of lower engagement. We also found evidence that as the reflection burden of the message increased, there were more disparities in engagement across participant characteristics. This finding helps inform who we may lose with content requiring more from users and thus how to ensure mHealth interventions do not widen existing health disparities.

Research focused on promoting mHealth engagement has proliferated in recent years, with the primary goal of increasing system use [30]. Across such studies, we see evidence that content that is more personalized; uses simpler, nontechnical language; and is empowering results in higher engagement [10,19,31-35]. Less research has compared specific types of content and has rarely tested different types within the same study. An exception is a recent study by Klimis et al [15], wherein they used machine learning to demonstrate that text messages with informative (providing health facts or education) and instructional (providing tips or recommendations) message intents were associated with increased engagement, while notification messages that addressed noneducational matters (eg, welcome and exit messages) were associated with reduced engagement [15]. Our study targeted a two-way message and varied the levels of reflection and response burdens in that message. By adjusting the reflection level specifically, we gained unique insight into how engagement with each message variation may ultimately influence behavior change [17,18]. The main way in which our study differs from others in this area of research is that we looked beyond system use as the sole dimension of mHealth engagement. Our goal was not necessarily to see which message resulted in the highest response rate but rather to determine how much reflection we could request from users and achieve a level of interaction that suggested that they were still invested in the content.

Although our results show generally that engagement decreases with more reflection, the nuances in our findings allow us to provide unique recommendations around mHealth design. For instance, it may be best to alternate through content with different levels of reflection burden. Although users were more likely to respond to content that was lower in reflection burden, nearly all (350/426, 82.2%) of the responses that we received to the high-reflection messages included a high-effort level of reflection. The act of asking people to reflect stimulates internal thoughts that are difficult to measure without a response [36] but may still occur among some persons who do not respond. Alternating content may help promote periodic responding and reflecting throughout an intervention experience. Another option involves using an adaptive intervention to tailor the content based on each person’s responsiveness. That is, everyone could start receiving content with a high reflection burden, but if a person’s response rate starts to drop, they could then switch to content with a moderate reflection burden. Finally, especially in situations where there is limited flexibility with the mHealth functionality, researchers may consider sending the medium/low message to all participants, given that the content encouraged a moderate level of reflection (more than the low/low message) yet still yielded a high response rate.

Our study has several limitations to acknowledge. For instance, our results are based on an SMS text messaging intervention, which is a specific form of mHealth. It is possible that users would have responded differently if the content was delivered via an app or wearable technology. Importantly, compared to apps and other internet-dependent technologies, SMS text messaging is both lower in cost and more easily accessed, and it tends to have higher rates of engagement [4,37]. In addition, this study recruited persons with diabetes and their support persons from a specific region in Middle Tennessee. We acknowledge that the findings may not be generalizable to other types of individuals who are living in other locations. Relatedly, the content asked about how the support persons supported the health of the persons with diabetes, and engagement may differ when asking about a user’s own health; however, the marked differences in engagement across message types support broader applications. Another limitation of our work is that we restricted our assessment of engagement to a behavioral measure (ie, responding to the text) and did not have a way to assess participants’ cognitive investment or experience with each version of the text. Based on our analysis of participants’ responses to the high/high message, it appeared that responders were cognitively engaged, but we were not able to compare cognitive engagement across the other messages. In addition, the sample size for the high/low message analysis (n=55) was considerably smaller compared to those for the other message analyses, which was due to testing the high/low message during only 1 wave near the end of the trial when fewer participants were enrolled. Relatedly, we did not have the time or a sufficient number of participants toward the end of the trial to test the medium/low and high/low text messages in a second wave, and we do not know for certain whether engagement with these texts could be impacted by temporality; however, as engagement with the high/high and low/low texts remained similar across multiple waves, it is unlikely. The ordering of the text messages was variable across participants, and due to the observational nature of this study, we cannot determine the extent that ordering may have impacted results; however, the average response rates and trends across message versions and waves provide general insights on how these variations may impact engagement. Finally, we did not assess the impact of engagement on outcomes, as this fell outside the scope of our study; however, other studies in digital health have examined this association [38,39].

In order for individuals to benefit from mHealth and achieve desired effects on outcomes, engagement with the mHealth tool is needed. Our results help elucidate how truly complex the nature of engagement is. Although our past work and that of others have demonstrated the importance of behaviorally interacting with mHealth interventions [9,31,40,41], this measure represents one piece of a larger puzzle. Engagement may be best conceptualized as including both a behavioral dimension and a cognitive dimension. Balancing these dimensions may be what is ultimately needed to achieve effective engagement for impacting intended outcomes. Our study contributes to a growing body of research that encourages a more nuanced approach to studying engagement that goes beyond measuring system use. We hope that our findings help advance the field of mHealth and inform intervention design, with the goal of optimizing both engagement and effectiveness.