The TAC Toolkit: Supporting Design for User Acceptance of Health Technologies from a Macro-Temporal Perspective

3.1.1 Selecting the Models of Technology Acceptance. Drawing on the acceptance literature, we selected validated models as the theoretical basis for the TAC toolkit. We first considered those models and extensions constituting the current theoretical foundations of technology acceptance: the TAM [20], TAM2 [98], TAM2’ [95], TAM3 [96], and UTAUT [99]. Next, we included models pertaining to pervasive technologies: the UTAUT2 [100], and PTAM [15]. Finally, we incorporated acceptance models devised specifically for the healthcare context: the HITAM [46], Hsu et al.’s model [41], Dou et al.’s model [27], Cheung et al.’s model  [12], Schomakers et al.’s model [79], and Dhagarra et al.’s model [23].

3.1.2 Identifying the Key Concepts across the Selected Models. In order to ground discussion among designers in pragmatic terms pertinent to real-world design choices, we chose to focus the TAC cards on antecedent factors, representing explanatory variables impacting user acceptance. Table 1 provides a complete overview of the 16 antecedent factors included within the final TAC card deck, along with their definitions, and models of origin. To maintain a clear focus on the health context, we additionally excluded those constructs highly particular to the use of technology for work (e.g. job relevance [98, 99]). Where models overlapped, similar constructs were regrouped as a single unique factor to facilitate their inclusion (e.g. reference group influence [12] and voluntariness to use [96, 98, 99] were regrouped under social pressure).

3.1.3 Developing the Cards’ Textual and Visual Content. Each card in the TAC deck¹ represents a single antecedent factor of technology acceptance, depicted on the front side in the form of a title and icon combination, intended to support memorability and the ability to easily distinguish cards from one another (see Fig. 1). Following both the common acceptance literature practice of categorizing acceptance factors [27, 46], and Alkhuzai and Denisova's design card heuristics recommending the grouping of cards and differentiation of groups using color  [2], we created three color-coded categories pertaining to Health (red), Individuality & Social context (orange), and Technology (blue), linking each of the 16 TAC factors to the category most closely related to their definition. This categorization was devised to both facilitate users’ familiarization with the cards and increase the learnability of the 16 acceptance factors.

Inspired by previous work concerning the value of sensitizing concepts [76] and interaction design tools intended to make frameworks (including for tangible interaction [81]) more accessible, we furthermore developed a series of thought-provoking, sensitizing questions pertaining to each factor (displayed on the back of each card). The first of these questions served to communicate the factor's definition in an accessible and engaging fashion, while the remaining questions encouraged deeper reflection in relation to different and specific aspects of the concept's definition. The cards were finally designed to resemble playing cards in support of user engagement.

The picture shows at the top a close-up view of the Social Pressure TAC card (captioned). The front of the card shows the icon symbolizing the factors (which represents an orange boiling kettle), and under it, the heading Social Pressure. The back of the card shows, at the top, a question in bold orange “How does society influence users’ health decisions?”, followed by a series of questions in normal font “To which social pressures are users exposed? Are these helpful? In what ways do our design choices lighten or lend weight to these pressures? Where does the technology place responsibility for users’ health?” and a bonus question “How might we design to help users make their choices and motivations their own?”. At the bottom, the TAC cards for antecedents Health beliefs and concerns (color-coded red) and Trust (color-coded blue) are shown.

3.2.1 The TAC Personas. We adopted the use of personas and scenarios as means of crafting a realistic context for reflection on technology acceptance on behalf of persons receiving health or mental health care, both as a means of providing examples of an implementation of the acceptance journey, and for enabling us to explore one possible use of the TAC cards in the design process. Through iterative collaborative design, we developed 3 personas², each associated with a respective scenario. While designing these personas, we aimed to ensure diversity of age, gender, and health concerns, creating three fictional characters living with common yet diverse health issues, for which technological solutions are often offered. These include Ella, a young woman and trainee solicitor diagnosed with type 2 Diabetes; Ali, an elderly bereaved spouse and retired florist, prescribed and struggling to manage antidepressant medications; and Alex, a middle-aged bus driver and father of three, worried about the possibility of catching COVID-19 and passing it on to his family. Each persona was defined in terms of information including demographic details (i.e. age, occupation, health status, social context), experience with technology, challenges faced, and personal traits that may influence acceptance of technology.

3.2.2 The TAC Scenarios. In parallel with these personas, we developed 3 scenarios³ designed to inspire engagement with the unfolding of each persona's interaction trajectory with a pertinent technology, namely a glucose monitoring sensor and app (Ella, Diabetes), medication reminder app (Ali, depression), or governmental contact tracing app (Alex, COVID-19). To account for the evolving nature of user acceptance over time, we emphasized the macro-temporal perspective of technology acceptance by employing the Technology Acceptance Lifecycle (TAL) timeline to structure each scenario in terms of the 3 consecutive stages of pre-use acceptability, initial use acceptance, and sustained use acceptance  [63]. The pre-use acceptability stage encompasses the period before any interaction with a technology occurs, but when both awareness and contemplation of its use surface. Thus, drawing also from previous work, 2 specific and critical temporal milestones in this stage were identified as seeking advice (a critical step in an individual's health trajectory [67]), and choosing technology (the decision to start using a health technology [86]). The very first interaction with a technology marks the end of pre-use, and the beginning of the initial use acceptance stage. Here, to facilitate exploration of a more granular time scale, we considered the following 3 temporal milestones: first interaction, next day, and a week later. Finally, in the last stage of sustained use acceptance, we considered the following temporal milestones: after 1 month, after 3 months, and after 1 year — the first 2 of which have been suggested as milestones for long-term acceptance in previous work  [98], while the last was added to reflect the lengthy or lifelong nature of many health conditions.

The picture shows a temporal scale divided into three stages: pre-use acceptability and initial use acceptance (distinguished by the ’First use’ time point), and sustained use acceptance. Some time in the sustained use acceptance stage, the time point Adoption demarcates the pre-adoption and post-adoption stages.

To support rich engagement on behalf of designers, we furthermore identified and described for each specific milestone 3 paths; each recounting acceptance issues of either high, medium or low degrees of challenge. For this, we drew inspiration from interactive narratives [3], where multi-choice scenarios have been employed in place of linear sequence stories or traditional linear scenarios. Thus, at each temporal milestone, designers can choose among 3 different paths that which they would prefer to explore (see Appendix A).

Design tools fostering empathy have long acknowledged the value of scenarios, in the mental health context in particular, from video stories [38] to vignettes, as means of describing the lived experience of ill health [74], or supporting therapeutic role-play [53]. To further elicit empathy in this case, both personas and scenarios were written in the first person, and employing believable, colloquial language. We aimed to furthermore increase empathetic engagement through the use of role-play, as previously employed to support the design of health technologies [53].

3.3.1 The TAC Think-Space. To enable designers to work collaboratively with the TAC cards in relation to specific design problems, we created a virtual board using the online platform Miro [58]. This think-space enabled participants to interact with the TAC cards in virtual-analogue form, displaying their front side only, in a collaborative digital space, at the same time as interacting with the physical deck. This space allowed designers to place selected cards against each temporal milestone of the user journey, while making notes reflecting their decision-making process to the side (Fig. 3).

The picture shows for each of the temporal milestones of the user journey, the cards selected by Group 5, together with their notes. The different elements of the picture are captioned.

3.3.2 The TAC Website. Finally, as multi-choice scenarios can be more effectively implemented digitally, we also developed the TAC interactive website [62] to host the digital personas and scenarios (see Fig. 4).

The picture shows a multi-choice scenario for the persona Alex's experience of a COVID-19 contact tracing app. On the left hand side, a vertical list of actionable buttons shows the 8 temporal milestones (i.e. seeking advice, choosing technology, etc. up to after a year). On the right hand side, three paths are made available to choose between, each marked as either low, medium or high degrees of challenge in relation to user acceptance. The cursor is hovering on the middle path. Buttons ‘next’ and ‘back’ at the bottom allow navigation between the steps.

5.1.1 Challenging Designers’ Preconceptions about User Acceptance. It was through challenging participants’ preconceptions of acceptance that the impact of the TAC toolkit was rendered most visible. In particular, designers commented often on the role of the toolkit in challenging a commonly-held assumption that the question of acceptance ceases to prove relevant once the user begins using the technology: “You made me realize that you have to consider acceptability at different points and that this acceptability may change because the needs of the user may change over time” (P14). Participants spoke then of coming to conceive of acceptance as a dynamic process, in line with the underlying theory [24, 32, 52, 63, 70, 80, 85, 89]. A participant with some prior familiarity with existing models of acceptance, explained: “It definitely makes you think about the technology [as] less static... something that needs to kind of grow and continue with this person and their needs” (P20). This comment suggests renewed awareness of the value of exploring acceptance across the entire user journey. This can in turn foster greater sensitivity towards the design of complex technologies, as required to accommodate users’ evolving needs.

Responses additionally indicate that the toolkit's timeline and cards’ three categories provided designers a means of visualizing this transformation of users’ needs. For example, on reviewing their final think-space board, P17 noted that “it is quite interesting how the ‘social context’ is at the beginning, and then the ‘health’ cards are at the beginning and end... and the ‘technology’ cards are all over [the user journey]”. This reflects an understanding of acceptance as extending beyond the pre-use stage and indicates an emerging practice among designers of linking the process of acceptance to the user journey: “It really helps to re-focus the design in a user-centered perspective all along, and going from the short [term]... to the use and adoption of the device in [the] long-term” (P9). This key finding suggests heightened awareness of evolving use and user acceptance over time, as further reflected in P14’s comment concerning the importance of accounting for the possible evolution of user needs: “when people are using it [the system], maybe we forget that we still need to make some adjustments”.

Some designers also reported that acceptance issues began to feel even more concrete in the later stages of the user journey, where issues become “tangibles, whereas in the beginning there's still a lot of too many [sic] intangibles” (P18). This was an impression described as further accentuated by the role-play component of the scenario: “It becomes more personal because I've now invested a year in this thing [technology]” (P5, playing the persona). These moments of insight pertained not only to the concept of user acceptance in a broad sense but also to the nature of health technologies in particular. This was highlighted by P1, a designer with a mixed HCI and psychology background, who pointed out that designing healthcare technologies was a complex process “with lots of different stages, and different stakeholders” and that therefore, the path to acceptance was likely to be longer than for other technologies.

Finally, engaging with the TAC cards during these sessions appeared often to nurture designers’ appreciation for, and challenge their understanding of acceptance factors in particular, leading them to develop a richer understanding of their definition and interaction, through reflection on the cards and conversation with other participants. P11, for example, speaking of the factor of ‘trust’, explained coming to understand that “it is not only about ‘trust’ as in ‘the data is safe’, but there's also other aspects that we should consider”.

5.1.2 Extending Designers’ Understanding of Technology Acceptance. The TAC toolkit also expanded designers’ perspectives on user acceptance, exposing factors that some wouldn't have otherwise considered: “I hadn't thought about all those forms of acceptance before, I think particularly the social ones” (P5). The number of factors influencing acceptance was also spoken of as a surprise by many designers: “I would never have thought of that many factors at play” (P6) and “I was not familiar with all these factors... My spectrum and my way of speaking changed around that topic” (P21).

Selecting positive user stories during the multi-choice scenarios made some designers realize that, even when ‘all is going well’, there may still be room for improvement in terms of user acceptance. As P14 commented, even if “everything went well, still there was a bone that you could try to address” — a point also reflected in Group 2’s notes made using the think-space “The user seemed to be enjoying/accepting the app enough to be prompting friends to install it. [Design action:] Include easy sharing mechanic to allow viral spread”. One participant furthermore reflected as to how “designers are trained to look at barriers” while there is also value to be found in amplifying positive elements: “I like the idea of choosing some of the positive stories... we can think about how could this ‘social support’ or ‘enjoyment’ of the technology be amplified?” (P1).

The multi-choice scenarios also helped designers picture the range of possible user experiences. P17, for instance, who was playing the persona and therefore had to pick a path at each scenario step, described how “it's quite interesting to see the different sorts of people that you may find”. Although real-world acceptance issues often involve a mix of factors, we initially asked participants to pick only one card per scenario step, to encourage negotiation and deeper conversation within groups, through trade-off-driven design [60]. While discussing cards for the first step however, all groups asked if they could select several cards, as they felt one wasn't sufficient to cover the factors at play. The facilitator then informed participants that they could pick multiple cards if they felt several factors were involved. We provided designers this autonomy during sessions in order to avoid creating an overly artificial study context. P20 commented: “if we'd only picked one, then maybe some important things wouldn't have been considered... we'd never have ‘privacy protection’ in there”. Group discussions furthermore revealed close relationships among factors, and their negotiation. Group 2, for example, discussed the interplay between ‘social support’ and ‘social pressure’ — “This support through pressure...  It's like the strategy to provide the ‘social support’ is ‘pressure’. It's why it feels so entwined” (P5). Participants also spoke of and leveraged the positive vs. negative impact of acceptance factors — “before it was a lack of ‘trust’ and now it's too much” (P13) — and suggested making this positive/negative outlook more visually explicit in using the TAC cards by, for example, flipping the card upside down on the board (Groups 1 & 2).

Participants additionally came to recognize developing an accurate understanding of users’ needs as a less than straightforward process. They did comment however that the TAC cards helped identify users’ needs: “I feel like users are very complex and it [the cards] were helping me maybe see the nuances” (P17), by “facilitating a faster understanding of what are the main targets, the main things to design for” (P11). One developer commented that “it's hard to design for a person as opposed to for a person's needs” (P4), elaborating that the cards allowed them to “turn this user into a set of experiences and actions” in order to find “the set of steps to solve this [acceptance] problem”.

5.1.3 Motivating the Application of Acceptance Theory through Playfulness. During interviews, the physicality of the cards was continually raised as a positive aspect of participants’ experience. In particular, most participants enjoyed the playfulness of the TAC toolkit and compared it to a game: “It felt like playing a board game, because the physical cards, the notion of placing things, the notion of choosing... gave a tactile nature to it that I really liked” (P4). We observed that this playfulness encouraged designers to translate acceptance theory into practice. P4 explains how the physicality of the materials made it feel as if they were ‘solving a mystery’: “Holding the cards, but in a way that the cards are telling a story... The mystery is how do we improve the user's journey with an app?”. The challenge of determining the influencing factors at each of a scenario's temporal milestones made the task meaningful and engaging: “It felt almost like we were trying to find the right answer. Even though there is no right answer, that's not the point” (P3), and additionally highlighted designers’ understanding that there is no exact truth — in that the factors selected depended upon designers’ interpretation of the scenario. Finally, participants felt satisfaction at being able to leverage the complex issue of acceptance, “touch[ing] on kind of the core components of a really complex problem and tech solution” (P7).

5.1.4 Supporting the Negotiation of Acceptance Factors. The physical externalisation of the selection process was furthermore described as helping participants determine which acceptance factors were, or were not, relevant to a given scenario: “I like physical stuff to touch, move around... To say ‘this card does not apply’, I'm literally physically gonna put it over here behind my monitor and not look at it” (P3). Participants typically began this decision-making process by considering all of the cards, usually face up, before making an initial selection of 3 to 6 cards deemed relevant for the factor at hand. They would then turn the selected cards over, read the sensitizing questions on the back, and discard the less relevant factors. This practice aligns with descriptions found within the broader literature of a simplified comparison process entailing twin stages of orientation or familiarization with the cards [5, 40, 60], and (re)framing of the problem space by selecting and discarding cards [5]. Some participants described arranging the cards spatially on their desk to prioritize the factors they judged most relevant to the scenario step in question: “I had them [the cards] on the keyboard... I could put them forward and backwards... to physically prioritize them” (P4).

Finally, the tangibility of the cards was commonly reported as both helpful and refreshing in the context of the hybrid setting. In particular, working with the physical cards appeared to encourage individual reflection, allowing participants to examine the factors and form their opinion at their own pace, while also selecting those they felt relevant without being overly influenced by the other designer's choices: “It frees your thinking when you have something tangible, and you're not just staring at a screen and other people, what they're picking out. I had my cards here in my hand. I felt quite free to pick as I wanted” (P6). Instances of physical interaction, from displaying cards to the camera to shuffling cards in hand, were often observed during the workshops — the combination of physical and digital appearing to render the experience more tangible and meaningful. The sensitizing questions on the back of the cards helped designers (in)validate their intuition about the acceptance factors at play, as reflected in a comment made during Group 5’s workshop: “I definitely think there's elements in the ‘self-image’ that is related to this situation, as in ‘Might the technology itself carry a medicalizing or even stigmatizing effect?’ [sensitizing question]” (P15). Finally, the 3 categories of cards furthermore shaped designers’ reflections in relation to acceptance at different points of the user journey. For instance, P17 (who played the persona) explained to their group: “In this stage, my main worries are about the ‘social context and individuality’ because I don't think I'm thinking about [the] technology per se”.

5.1.5 Shaping Designers’ Practice to better Account for Acceptance. During the interviews, designers mentioned a number of ways in which the TAC toolkit could shape their future design practice. Several participants explained that they would use the kit to stimulate their own reflection on acceptance “not only design for a specific goal, but also really think about how this [technology] can be integrated in someone's life” (P17). For P1 (with a background in psychology), the cards would be useful for “think[ing] a bit more broadly about the technology side of things... when I'm brainstorming”. Other designers mentioned that the cards helped them to reflect on their own design practice: “I'm more aware of acceptance as a thing that I need to consider in design... maybe use the cards to make sure I was really thinking of it” (P20). Similarly, P6 (a clinical psychologist) commented that they would use the cards to guide design conversations in an interdisciplinary environment, by having “these to hand in that kind of design phase to ensure that we're having the right conversations”. This comment implies the need for tangible support to orientate discussion of user acceptance within interdisciplinary settings.

Finally, although the cards were initially framed for use by designers, several participants commented on the potential of the toolkit to facilitate conversations with users in two ways. It was described as potentially supporting the elicitation of user needs “maybe if you bring cards with examples, they'll start to think deeper about these factors, they'll realize ‘Oh, this might actually be important for me, now that you've brought it up’” (P10). It was suggested that the TAC cards might require several adjustments however (e.g. ‘with examples’) to fulfill this aim of eliciting users’ needs and to be successfully employed with users, such as “mak[ing] a simplified version, perhaps for users, that has different questions” (P1). An alternative approach suggested by P3 was to employ the cards as a means of ‘priming the conversation’ with users. Group 1’s workshop provided an example of what leading a conversation with the TAC cards could look like: Designer P2 asking User P1 “Between ‘health beliefs and concerns’ and ‘self-image’ what do you think, Ali [persona], is more critical here for you?”.

5.1.6 Adopting a more Ethical Approach to Design for Acceptance. Researchers have more recently also begun to acknowledge the association between technology acceptance and ethical design (e.g. in value sensitive design [4]), including ethicality as a factor in user acceptance — motivated in part by the acceleration towards digital healthcare driven by the COVID-19 pandemic, and the enforcement of governmental contact tracing apps [64, 65, 87]. Paska, for example, argues that “technology acceptance models should also take into account the ethical aspects of technology in terms of how technology shapes the image of today's world” [64]. Although the TAC cards didn't include this ethicality factor, the workshop activities led designers to consider ethical principles while envisaging solutions to user acceptance issues.

At each scenario step, participants were asked to think of ‘design actions’ which might be taken to address the user's acceptance challenges. A large number of the design choices suggested by the groups coincided with the transdisciplinary ethical principles developed by Bowie-DaBreo and colleagues [9]; Transparency, as evoked by 4 groups (e.g. “an indication of how reliable the [glucose sensor's] results are”, Group 4); Autonomy, mentioned by 3 groups (e.g. “allowing user[s] to stay in control proactively (not reactively)”, Group 3); Accessibility, recommended by 2 groups (e.g. “make the (small) fonts adjustable so users with all requirements/ages can read it”, Group 5); And Privacy, discussed by a single group (“notifications are [kept] general to protect privacy”, Group 7). Finally, in line with the move towards more personalized health and mental health technologies, recommendations for more tailoring of the technology were made across 4 groups (Groups 3, 4, 5 & 7).

5.2.1 Facilitating Reflection around Acceptance. As our participants noted, multiple obstacles stand in the way of designers’ capacity to reflect upon and engage in discussion of user acceptance. Firstly, technology acceptance is an ‘immense research field’ (P11), and the multitude of theories can prove overwhelming. By translating these theories into a relatively concise framework, the TAC cards created a defined space for designers to approach theoretical constructs:

« I've come across 15 theories myself... slightly different perspectives depending on the context... A set of generalizable or standardized questions that could be asked for general constructs that are suggested in those different theories, it's a really useful tool to have. » P16

Workshops furthermore revealed that designers lacking familiarity with user acceptance often refrain from taking part in design conversations if they feel they have ‘nothing to bring to the table’. The TAC cards, in this regard, created a safe environment, helping designers feel more confident in discussing acceptance: “I could be an important part of the discussion, on equal terms with the others” (P11). Another challenge for designers new to the concept of user acceptance is understanding the numerous individual aspects of the concept: “You have to remember that there could be all these different things at play” (P1). The issue here is two-fold: on the one hand, designers might not remember all acceptance factors and fail to address key elements in technology design; on the other hand, they might overly focus on a subset of acceptance factors, and overlook others relevant. Trying to remember these theories furthermore adds to designers’ cognitive load. While the TAC toolkit helps tackle these issues, we also observed the presence of a learning curve during participants’ first use of the cards, as reflected in P20’s comment that “initially, it was a little overwhelming... as time went on, you became more familiar with them”.

The toolkit was also described as lending a concrete dimension to the concept of user acceptance, often perceived as too abstract, by operationalizing the acceptance factors in a form easier to grasp and apply in design: without the moderation of the cards, when I think about user acceptance, well I think about it at a very abstract level... it kind of helped navigate our thinking to one certain area in depth (P15). When participants were unsure about the meaning of a factor, the sensitizing questions at the back of the cards provided clarification (P2). Similarly, when a factor's title appeared too vague or ambiguous, designers checked their interpretation against the questions provided: “my computer science brain obviously assumed ‘integration’ meant compatibility across technologies, but really it was ‘life integration’” (P3).

5.2.2 Opening New Perspectives through Interdisciplinary Collaboration. The interdisciplinary setup of the groups also appeared to benefit designers’ reflection, some participants reporting that the collaboration exposed factors they hadn't considered: “I could see some aspects from a scenario that I wasn't considering, that came with the collaboration” (P19). During interview, P6 further explained how working in an interdisciplinary group broadened their own perspective: “[P5] saw things a different way. So, it definitely widened my perspective on how people can feel about a technology”. The value of involving psychologists in acceptance conversations was also underlined by P20 (clinical psychologist), particularly in order to discern nuances in users’ behaviors and thought processes, and identify manifestations of mental health difficulties.

6.1.1 Leveraging the Temporal Continuum: Pre-Use Acceptability — Initial Use Acceptance — Sustained Use Acceptance. Nadal et al.’s prior review showed that user acceptance was rarely examined at the pre-use stage [63]. In addition, user journeys tend to focus on users’ interactions with the technology (e.g. patient journey mapping looking at patients’ ‘touchpoints’ with healthcare technologies [56]), thus failing to consider users’ perceptions of the technology. The TAC toolkit aimed to tackle this possible oversight by showing that the user acceptance journey consists of a sequence of experiences, each susceptible to changing the user's perception of the technology. Participants observed this connection when Persona Ella took on the glucose monitoring app:

Ella (P8): « Setting it all up was easier than I expected. The sensor is attached to my stomach, just above my hip. It's a bit weird but it's discreet. I'll get used to it... 

P9: The ‘technology anxiety’ she [Ella] has has been suddenly reduced.

P7: Yeah, there's a sense of ‘enjoyment’ in terms of [the app] being initially usable, easier than expected. »

Furthermore, most studies measuring acceptance have focused on the sustained use stage [63], evaluating the extent to which users have accepted the technology after long-term use. This approach reduces acceptance to a point measure, which does not capture the evolution of user experience. Measuring sustained use acceptance also requires deploying the health technology, potentially with a clinical population. This is a more taxing process for gaining insight into acceptance problems that could have been identified earlier in the course of design. The TAC toolkit as an exploratory design tool, thus used at an early design stage, enabled designers to look into prospective user acceptance issues with a system, and understand how design choices could lead to a particular user acceptance trajectory. P20 explained that, in the sustained use stage of the workshop, they noticed that “[the persona] is still in the same [problematic] place: what does that mean?”. They then reflected on the acceptance factors the group had flagged as relevant in the previous steps of the user journey: “we had picked that before and now he [the persona] is here. So, you know, what do we need to think of for the technology?”.

7.4.1 Integrating Design Tools for Bridging Acceptance Theory and Design Practice. Findings indicate the value of the TAC toolkit for articulating and leveraging theoretical HCI work on technology acceptance in order to better inform the design for acceptance of health technologies. The significant need within HCI for bridging the gap between theory and design practice has been long acknowledged, and efforts to address it have led to conceptual contributions, such as translational resources [13, 14], intermediate design knowledge, strong concepts [39], bridging concepts [17], boundary objects, [94], or implications for design [76]. However, despite the progress made at a conceptual level and the wealth of traditional design tools, those for better bridging the gap are still much needed. We argue that the value of the TAC toolkit resides in the integration of exploratory design methods, such as personas and scenarios, with the TAC cards, and within the think-space and website. While personas and scenarios have been traditionally coupled in design research [16, 25], our findings suggest the added value of integrating these with acceptance theory, operationalized through the TAC cards and their sensitizing questions.

7.4.2 Considering the Evolution of Acceptance Factors in Designing Tools for Acceptance. Another implication for design tools supporting long-term acceptance of health technologies is accounting for how the factors of acceptance may change over time. This has been reflected in the evolution of acceptance models, moving from a focus on technologies for the workplace [20, 21, 88, 95, 96, 98, 99], through pervasive technologies [15, 100], to healthcare technologies [23, 27, 41, 46, 79]. Our findings also provide empirical support for ethicality as an emerging antecedent of user acceptance [64, 65, 87]. This is a clear indication that, while the TAC cards comprise an effective capturing of today's most relevant antecedent factors, they will benefit from future revisions in order to align with evolving technologies and their users’ needs. The TAC toolkit is itself finally a key contribution of this work, which we make available to designers and researchers for adoption and adaptation to the unique context of their own health technology designs.

7.4.3 Supporting Design for Long-Term Acceptance. Unlike the exploration of user acceptance challenges before and at the early stages of use of the technology, considering distant user acceptance issues (in the sustained use stage) proved challenging. This related to the less familiar task of envisioning the long-term evolution of user experiences. Despite these challenges, designers appreciated the importance of such future experiences, and highlighted the value of a longer design activity to address those. Previous findings in cognition research showing that future events can be better imagined and pre-experienced when they are positive, and rich in sensorial details [28], we can imagine temporal multi-choice scenarios that are likewise richer in sensorial details to support designers in this task.