Abstract
Objective
To explore the practices, perspectives and beliefs of clinicians treating adolescents with nonspecific persistent back pain.
Design
A qualitative descriptive study using individual, semi-structured interviews. Reflexive thematic analysis was used to code interview transcripts and generate relevant themes.
Setting
Clinicians in any clinical setting where adolescents with nonspecific persistent back pain are treated.
Participants
Ten clinicians (eight chartered physiotherapists, one nurse and one psychologist) who currently treat or have treated adolescents with nonspecific persistent back pain.
Results
Five themes were identified which captured the practices, perspectives and beliefs of clinicians treating adolescents with nonspecific persistent back pain: (1) Multiple relationships, one priority, (2) Without buy-in, it won’t work, (3) Managing pain, living life, (4) No one-size-fits-all treatment, and (5) Who you see is what you get.
Conclusions
Treating an adolescent with nonspecific persistent back pain is not the same as treating an adult with the same condition. Specifically, clinicians must attend to the needs, concerns and beliefs of both adolescents and their parents, reflecting the diminished autonomy of adolescent patients. Clinicians tend to offer person-centred care to adolescents with nonspecific persistent back pain. However, they currently lack guidance on how to foster effective treatment relationships with parents and how to achieve buy-in to a modern conceptualisation of persistent back pain as a biopsychosocial phenomenon.
Persistent back pain is a global health problem affecting millions of people across age groups. 1 According to an analysis of more than 600,000 adolescents in 33 countries or regions, the prevalence of persistent back pain in youth aged 11 to 15 has increased from 18.3% in 2001/2002 to 21.6% in 2013/2014. 2 In a study that included more than 6000 students aged 14 to 19, Masiero et al. found that of the 2549 students who reported at least one episode of lower back pain, more than 40% consulted a healthcare professional about their pain. 3
Adolescence is a life stage defined by change, when children experience rapid growth 4 and transition between social and emotional dependence and autonomy. 5 Research on adult nonspecific persistent back pain has steadily evolved to emphasise the biopsychosocial model,1,6 and clinical guidelines for treating adult nonspecific persistent back pain reflect that change.7–9 However, the evidence base for treating adolescents with nonspecific persistent back pain remains sparse and may not reflect a modern view of such pain.
Previous research on adult musculoskeletal pain has identified systemic, personal, and societal barriers that may prevent clinicians from promoting and acting in accordance with a biopsychosocial view of persistent pain.10,11 Clinicians treating paediatric patients with persistent pain may lack education about the modern biopsychosocial conceptualisation of such pain. 12 Comfort with explaining the psychosocial aspects of pain to patients and families may also play a role. In a qualitative survey asking 233 Swiss paediatricians to explain the causes of a 14-year-old case vignette's persistent musculoskeletal pain, even those who identified psychological and social factors as the explanation were likely to centre their conversations with the patient's family on biological factors. 13 Thus, we wanted to learn directly from clinicians about their experiences treating adolescents with nonspecific persistent back pain to understand more deeply their beliefs about and their methods of working with this population. The aim of this qualitative interview study was to undertake an in-depth exploration of clinicians’ practices, perspectives and beliefs related to treatments for adolescents with nonspecific persistent back pain.
Methods
This was a qualitative semi-structured interview study designed for use with reflexive thematic analysis. 14 The study was approved by the University of Limerick Faculty of Education and Health Sciences Research Ethics Committee on 13 December 2023 (study #2023_09_19_EHS). The Consolidated Criteria for Reporting Qualitative Research 15 guided this report.
Participants were purposively recruited via both public social media posts and private direct messaging. Clinicians in any field (e.g. paediatricians, physiotherapists, clinical nurse specialists) who had previously treated, or were currently treating, an adolescent (aged 12 to 17) with nonspecific persistent back pain were invited to participate if they spoke sufficient English to participate fully in the interviews. All authors posted recruitment fliers on their social media channels, including Facebook, X (formerly Twitter) and LinkedIn. Professional colleagues in nursing, physiotherapy, psychotherapy, occupational therapy and general medicine from Australia, the UK and the United States shared the recruitment posts within their networks. Recruitment took place from December 2023 until late February 2024. All participants were over age 18 and provided verbal informed consent prior to participating.
Eligible, consenting clinicians were interviewed by SDH individually via the online meeting application Microsoft Teams between 5 January and 22 February 2024. Each interview was recorded and lasted from 28 to 55 min, and each participant was interviewed only once. Participants and SDH had no relationship prior to the study. However, each participant was introduced to SDH via email prior to the study, and the first few minutes of each interview were used to establish rapport and participant comfort with SDH. In addition, SDH explained to participants that treatment for adolescents with nonspecific persistent back pain was the primary topic in her doctoral research.
In keeping with a reflexive methodology, SDH used the interview guide as a starting point (see Supplemental File MethodsS1) but allowed the interviews to flow in the topical directions the participants initiated, as long as they remained relevant to the study aim. In this way, interview data were incredibly rich and interesting. Braun and Clarke16,17 encourage researchers using reflexive thematic analysis to avoid positivist methods of predetermining an adequate sample size and eschew the concept of ‘data saturation’ as incompatible with reflexive analysis. Therefore, we elected Malterud et al.'s concept of ‘information power’ to determine when an adequate sample had been reached, based on the depth and breadth of data collected in relation to our specific aim. 18 A total of 10 interviews was considered adequate to provide a quality reflexive thematic analysis. Participants did not receive any remuneration or incentive for their time. Interview transcripts were not returned to participants for their comments, as ‘member checking’ is incompatible with a reflexive thematic analysis. 14
Reflexive thematic analysis emphasises the important positionality and situatedness of the researcher in the research process. 14 The corresponding author and lead researcher (SDH) has found that her extensive training as a wellness coach and master's degree in interpersonal communication have the effect of helping strangers open up to her, even about sensitive topics. Such personal characteristics and professional skills have led SDH to a contextualist epistemology, in which there are truths in the world, but those truths exist in context and are couched in each person's unique exposures to social and cultural environments and experiences. 19 This, in addition to a critical realist ontology, 19 placed SDH in an active, analytical position during the entire research process. See Supplemental File MethodsS2 for a complete description of data coding and analysis.
Methods of assessing the quality of a reflexive thematic analysis should be consistent with a reflexive, rather than a positivist, approach to data analysis.17,20 To undertake a high-quality reflexive thematic analysis, ‘procedures like organic and open-ended coding, theme review and refinement and the recursivity of the analytic phases’, 17 (p.19) are recommended. In line with these recommendations, SDH engaged in continuous reflexivity throughout the analysis process, regularly revisiting original transcripts and comparing new readings to earlier reflexive field notes.
This being a ‘big Q’ qualitative approach, such practices as inter-rater reliability and controlling researcher bias were not appropriate. 21 We have addressed the concept of rigour in accordance with Finlay by showing that the analysis was ‘completely managed and systematically worked through’ and that the ‘findings match the evidence in a convincing way’. 22 (p.110)
Results
Ten clinicians completed interviews. Another seven initially expressed interest in participating, but five dropped out due to unknown reasons prior to consenting, and two were ineligible. Participants ranged in age from 23 to 56 years and had from 1.5 to 30 years of clinical experience. Nine participants were working in Ireland and one in England. Two clinicians saw paediatric patients (aged 17 years or younger) 50% of the time, while most participants worked exclusively with paediatric patients. Eight participants were chartered physiotherapists, one a nurse, and one a psychologist.
Five themes were developed in this reflexive thematic analysis of clinicians’ practices, perspectives, and beliefs related to treatments for adolescents with nonspecific persistent back pain: (1) Multiple relationships, one priority, (2) Without buy-in, it won’t work, (3) Managing pain, living life, (4) No one-size-fits-all treatment, and (5) Who you see is what you get.
Theme 1: Multiple relationships, one priority
Many clinicians initiated their interviews by describing the central role of relationships in their treatment of adolescents with nonspecific persistent back pain. Most adolescent patients are legally required to be accompanied to healthcare appointments by a caregiver, so effective treatment depended on the clinicians having good relationships with both parents and adolescents. This added complexity to the treatment process, as clinicians worked hard to prioritise the adolescent's needs. They described thoughtfully facilitating parents’ optimal involvement in the adolescent's treatment and getting parents and their child aligned in terms of goals and treatment approaches. In paediatrics, it's not just the relationship with the child, but it is the relationship with the parent, and then also looking at the relationship between the child and the parent and how you can get them to work as a team rather than batting against each other. (Clinician 8)
Participants shared examples of prioritising the adolescent's voice in the treatment sessions to make sure they felt seen and heard, such as telling parents: ‘As you're not the one actually experiencing the pain … I'll come to you in a minute. But can I hear what my client's got to say first?’ (Clinician 5). However, parents’ perceptions of their adolescent's pain were brought into the child's treatment sessions, and clinicians described having to educate the parent, engage the child in direct treatment, and ‘explore [parents’] role in the treatment plan’ (Clinician 8). To that end, Clinician 9 even prompted parents of younger adolescents to ‘get down on the floor and do [the treatment exercises] … with them’ if the child needed encouragement at home.
This dynamic of managing the parents’ needs in addition to those of the adolescent was a source of frustration for some clinicians, such as Clinician 4: ‘I love working with kids, but sometimes the parents are the ones that it's like, alright, aaagh [frustrated vocalization]’. However, working with parents was described as a necessary part of meeting the treatment needs of the adolescent patient, despite the potential frustrations. If parents felt their own views or preferences were not being taken seriously, they might not bring their adolescent to treatment sessions at all. To foster such positive relationships, Clinician 9 said that treatment sessions could become more like ‘counselling sessions’, where communication must be open, and sensitive topics could be discussed safely between all parties.
Theme 2: Without buy-in, it won’t work
Clinicians also described how both adolescents and their parents must buy in to treatment for it to succeed. Buy-in matters because, across the board, clinicians were dedicated to getting adolescents and their parents out of the seemingly pervasive ‘pain equals damage’ mindset. Physiotherapists emphasised with patients that movement was safe and, in fact, not a danger to their back even when it hurt. Clinicians on a multidisciplinary team encouraged a broader view of pain, where educating the patient and parents about persistent pain, its biopsychosocial nature, and how it differs from acute pain was a major step in achieving buy-in: ‘The initial stage of treatment is definitely a reframing [of pain] … trying to de-threaten the feeling of pain and helping them explore … what other factors are contributing to this experience’ (Clinician 2).
The adolescent-parent dyad's previous exposure to other clinicians could make it more difficult for a clinician whose treatment adhered to a biopsychosocial perspective. For example, Clinician 10 explained that if a previous clinician had done imaging and found no physical or structural cause for the adolescent's pain, they might use words like ‘There's nothing there [in your body], therefore, it's in your mind’.
Clinicians thought that adolescents advanced more quickly through treatment if they were receptive to understanding connections between stress, life events and their pain experience. They also believed that parental buy-in to this connection would increase adolescent acceptance of non-physical pain factors. Clinician 8 explained, ‘If you have a parent who can recognise … that, actually, yes, [the pain] can be related to something other than what's going on in their body, I think [adolescents] are more likely to take it on board’.
Clinician 3 concurred, explaining how when a parent had already bought into the idea that there was no structural cause for their adolescent's back pain, that buy-in allowed him to gently suggest that the adolescent be referred to a psychologist for care when distress over her symptoms became extreme. ‘The mother was bringing up the psychosocial aspects with me anyway, so I knew she was open to that side of treatment being explored, and I was able to have that conversation’.
In the multidisciplinary pain programme, a key issue with achieving parental buy-in seemed to be the naming of their adolescent's condition as ‘persistent primary back pain’. Clinician 10 explained how their treatment may not differ much from what is offered in community settings, but their team has the benefit of saying to parents, ‘This isn't a mystery anymore. We know the treatment for this [condition], and this is what [the treatment] is’. That diagnosis process served to validate parents, which in turn increased their likelihood of treatment buy-in.
Theme 3: Managing pain, living life
Many clinicians stated that for adolescents with nonspecific persistent back pain, the primary goal of treatment is to improve functioning and manage pain, not necessarily reduce pain. As Clinician 6 described it, ‘OK, the pain is there, we all acknowledge that, but let's see what you can be doing as well … we need to get you back living’. These views were shared by Clinician 2: ‘I'm always hoping that pain has gone, you know “I don't feel it anymore”. But I suppose what I'm … also hoping to hear is that “It doesn't get in the way of me doing things the way it used to”’.
Participating clinicians used outcome measures that focused on function to show that life could proceed even though pain was frequently present. They described working with parents to change their perspective towards function rather than pain. ‘We really have to try and support [parents] to think about their decisions, that they're making decisions to sort of build life, not to reduce pain’ (Clinician 10). Reducing the fear of pain was cited as vital, with several clinicians using exercise to show patients and their parents that moving in specific ways was not ‘gonna cause some sort of irreparable damage’ (Clinician 3) in the child's back.
This emphasis on increased function rather than pain reduction was described by clinicians as a lifelong strategy for adolescents to self-manage pain. Part of treatment involved conveying to adolescents that back pain is a normal part of life and should not prevent them from proceeding with their lives. ‘I don't let them shy away from [activities] that increase their pain, if they're tolerating it in the end, they're happy with some of the trade-offs that they might get from some of the psychosocial benefits’ (Clinician 3). Participation in school was viewed as particularly important, with clinicians sharing strategies such as ‘movement breaks’ (Clinician 4) and ‘modified PE [physical education]’ (Clinician 6) to help adolescents stay engaged with their peers despite pain.
Theme 4: No one-size-fits-all treatment
In every interview, clinicians described treatment approaches that were individualised and person-centred. They assessed the person in front of them and devised treatment only after ‘making sure there's some goals established’ (Clinician 3). This clinician went on to say that by deferring to the adolescents’ goals, ‘they make you create the treatment as opposed to you imposing the treatments’. Because of this individualised approach, participating clinicians mentioned a broad range of treatments that they have used with this population, including many forms of physical activity and exercise, activity modification, orthotics, medication, pain education, relaxation and stress management, and, for the clinicians on a multidisciplinary team, a multidisciplinary-team approach.
It was common for participating physiotherapists to encourage the adolescent to engage in physical activity as a part of their treatment, but the choice of activity would be driven by the child: ‘A big part of the program really is trying to get them to find an activity that they enjoy, that's fun, that they will be able to continue’ (Clinician 8). Some clinicians acknowledged just how challenging of a time adolescence was, and every participant expressed ways in which they ‘meet [the adolescent] where they’re at’ (Clinician 4) so their treatment is bespoke and relevant to that child. Similarly, another clinician gave an example of delaying the introduction of exercise as treatment in response to an adolescent's specific needs. Like one recent kid I had in … everything was pain focused …. We did three sessions before I even introduced exercise, and her pain had improved within those three sessions. Because the way she came in to me, had I just given her exercise, I think … we wouldn't have gotten anywhere. (Clinician 8)
Even within the particular multidisciplinary-team programme in which some study participants worked – which they described as initiating with a standardised 2-day program that prioritises pain psychoeducation – clinicians talked about how the goals, values and realities of the adolescent and their family drive the whole treatment. One clinician explained that the team, at the beginning of the programme, is investigating all aspects of the adolescent's life prior to designing a treatment plan: ‘[We are] looking at things like school, physical activity, their social lives, sleep and any other family or life stressors that could be present and … the whole family are invited to share information about that …’ (Clinician 2).
Theme 5: Who you see is what you get
In their interviews, clinicians revealed that the range, and order, of treatments they offered reflected their own training and experience. Difficulties and delays when referring patients to multidisciplinary colleagues or specialist pain programmes were common. This meant that clinicians frequently practiced within their own professional comfort zone, even when other issues were evident.
For physiotherapists, the initial treatment strategy typically involved function-based exercises and either increased or modified physical activity. Having access to a multidisciplinary team, one physiotherapist took a broader approach, assessing everything from sleep hygiene to screen time to social participation. But ultimately, the treatment plan was ‘very much exercise-based therapy’ (Clinician 7). When initial exercise-based treatment didn’t seem to be working, one physiotherapist described how he always tried to modify his exercise plan before seeking out referrals to other disciplines, such as psychology. If they're still getting this huge pain response at home that I'm just not finding in the clinic, I start to wonder about other [psychosocial] things going on …. But I usually first try to think that actually, the problem's me, with what I'm coming up with …’. (Clinician 3)
Most clinicians acknowledged that nonspecific persistent back pain was not just a ‘back’ problem; it was biopsychosocial in nature. However, when psychosocial stressors appeared to be within the family, independent physiotherapists were sometimes put in a difficult position if referral to a psychologist was not possible, because parents were legally required to be present at physiotherapy appointments. It can be quite difficult to address [psychosocial factors]. … If the relationship between the parent and the child isn't great, and that could be influencing [the child's pain], [it's] very hard to bring that up or to delve into that, which is where [a referral to] psychology would be great, because obviously they [the child] do go in [to appointments] on their own to psychology. (Clinician 4)
Overall, though, independent physiotherapists had not been trained in how to handle conversations about psychosocial aspects of pain. Instead, these conversations were managed according to what the clinician and the patient seemed comfortable with. ‘Are you coping OK?’ is one way I'll ask it, or … ‘How are you feeling about it?’ … If they're open to talking about it, I'll let them talk about it for a while, and if they say ‘No, I'm coping fine,’ I don't probe it any further there, but I might revisit it at a subsequent session. (Clinician 3)
This method contrasted markedly with clinicians in a multidisciplinary team. This programme features a team-based method for approaching persistent back pain as a biopsychosocial phenomenon, and pain psychoeducation for the parents and adolescents forms the foundation of treatment. Each multidisciplinary team member—including psychologist, occupational therapist and clinical nurse specialist—brings their own specialised training and education to the patient's comprehensive treatment.
Discussion
Overall, the five themes generated from these clinician interviews showed that treatment for adolescents with nonspecific persistent back pain is not simply about fixing a problem in the adolescent's back. Rather, key aspects of treatment are fostering good relationships, educating patients and parents about the mind-body nature of persistent pain, and prioritising the adolescent's goals, values and beliefs. The presence, beliefs and needs of parents greatly influenced the complexity of treating these adolescents. Across the interviews, improving function was shown to be a core goal, while the particulars of treatment varied depending on which clinician the adolescent saw and in which setting.
The central role of the adolescent–clinician relationship in treating adolescents with nonspecific persistent back pain echoes Davison et al., 23 who found that adolescents want a trusting, collaborative relationship with their clinician. In our interviews, clinicians also described how important the parent–clinician relationship was in the treatment process. This was surprising, as most randomised trials for this population have not been designed with relationships as a central input, nor have they targeted parental involvement. 24 Recent qualitative research highlights the importance of involving the family in treatment for children with chronic non-cancer pain, 25 while clinical guidelines state that the child's ‘health needs, preferences and expectations’ should be prioritised even above other needs of the family at large. 26 (p.ix) Clinicians described challenges associated with balancing both parent/family needs and the adolescent's needs.
Participants also believed that both adolescent and parent buy-in to treatment could affect treatment success. Buy-in to modern approaches to chronic pain treatment, such as the multidisciplinary and biopsychosocial approaches featured in our clinicians’ interviews, could be interpreted as harmful or illogical by parents who believe the cause of their child's back pain is structural. 27 Without buy-in, parents could take their child elsewhere, searching for what they deemed a more suitable diagnosis or treatment. Unfortunately, parents looking for treatment guidance online are likely to find messages encouraging them to continue seeking a satisfactory ‘anatomical’ diagnosis for their adolescent's nonspecific persistent back pain. 28 Likewise, young people with chronic pain who believe that ‘an injury hasn’t healed’ or ‘something is wrong with my body’ 29 may be too fearful to engage in exercise, or they may judge an exploration of their current stressors to be irrelevant to treating back pain. More research is needed on how to communicate the mind-body nature of persistent pain in an acceptable way.30,31
As a treatment goal, the clinicians in our study primarily aimed to help adolescents manage their nonspecific persistent back pain so they could fully re-engage with a meaningful life, rather than focus solely on pain cessation. These goals are consistent with a multidisciplinary team approach to disabling persistent pain. Multidisciplinary treatment intentionally addresses a range of biopsychosocial outcomes. 32 However, while youth (aged 11 to 18 years) undergoing treatment for musculoskeletal pain prioritised increased overall functioning, parents focussed more on pain reduction. 33 Counselling and additional education prior to initiating treatment may be needed to align patients and families on treatment expectations and goals. 34
To reach the goal of helping adolescents with nonspecific persistent back pain live life despite pain, all clinicians described treatment that was individualised and driven by the expressed goals and needs of the patient. This finding aligns with the recent emphasis on person-centred care for the rehabilitation of low back pain in both adults and adolescents.35,36 The first of four guiding principles in the most recent World Health Organization guidelines for non-surgical management of chronic back pain in adults is ‘Holistic and person-centred care’. 8 Taken together, those guidelines recommend a ‘comprehensive, tailored approach’ to treatment. 37 Interviewed clinicians seemed to use that approach with adolescent patients as well, and only after a thorough clinical evaluation had ruled out specific causes.
Our final theme, ‘Who you see is what you get’, illustrated that the method and order of delivery of treatment components varied by clinician training and setting. This theme recalls Cherkin et al.'s studies of physicians’ variation in diagnostic testing and treatment choices for adult low back pain.38,39 The authors found that the type of diagnostic test physicians ordered varied according to their training or clinical specialty, and many physicians’ treatment choices were not supported by evidence. Because rigorous research on treatment for adolescents is still in its nascent stages, their clinical care may be as clinician dependent as care for adults with low back pain was 30 years ago. Our findings illustrate the urgent need for large-scale, methodologically robust trials to build the evidence base for treating adolescent nonspecific persistent back pain.24,32,40
Limitations to this research should be noted. This study is a reflexive thematic analysis, meaning that SDH's subjectivity and interpretation of the data were an integral part of the analysis. 21 In addition, the only eligible clinicians who consented to participate were located in either Ireland or the UK and were either physiotherapists working in public or private practice or clinicians (physiotherapist, nurse, psychologist) in a multidisciplinary team. Responses from clinicians in other locations and in different areas of healthcare practice may have diverged from those of our participants.
In sum, participating clinicians described treatment of adolescents with nonspecific persistent back pain that was individualised and person-centred. They also identified aspects of treatment which have not yet been considered in intervention research. Until high-quality trials provide evidence to guide clinicians in these aspects of treatment, challenges such as those identified by our participants will persist.
Clinical messages
Adolescent patients’ parents play a key role in the treatment of nonspecific persistent back pain.
Proven methods for eliciting parent buy-in to biopsychosocial or multidisciplinary treatment methods are needed.
Treatment for adolescents with nonspecific persistent back pain may be clinician dependent because evidence lags far behind that for adults.
Supplemental Material
sj-docx-1-cre-10.1177_02692155251324589 - Supplemental material for ‘It can be very complicated’: A qualitative analysis of clinicians’ practices and perspectives on treating adolescents with nonspecific persistent back pain
Supplemental material, sj-docx-1-cre-10.1177_02692155251324589 for ‘It can be very complicated’: A qualitative analysis of clinicians’ practices and perspectives on treating adolescents with nonspecific persistent back pain by Sara D Hauber, Katie Robinson and Kieran O’Sullivan in Clinical Rehabilitation
Supplemental Material
sj-docx-2-cre-10.1177_02692155251324589 - Supplemental material for ‘It can be very complicated’: A qualitative analysis of clinicians’ practices and perspectives on treating adolescents with nonspecific persistent back pain
Supplemental material, sj-docx-2-cre-10.1177_02692155251324589 for ‘It can be very complicated’: A qualitative analysis of clinicians’ practices and perspectives on treating adolescents with nonspecific persistent back pain by Sara D Hauber, Katie Robinson and Kieran O’Sullivan in Clinical Rehabilitation
Footnotes
Author contributions
All authors developed the study topic and recruited participants. SDH interviewed participants and completed data analysis. SDH discussed and refined the results of the analysis with the help of KR and KOS. All authors edited and commented on drafts of the manuscript and approved the final draft.
Consent to participate
All interviewed participants provided informed consent prior to participating.
Data availability
The dataset generated during the current study are not publicly available due to the authors not requesting such from the University of Limerick, Faculty of Education and Health Sciences Research Ethics Committee. However, the anonymised dataset is available from the corresponding author on reasonable request.
Declaration of conflicting interest
The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: KOS provides continuing education workshops for healthcare professionals on the assessment and management of persistent back pain. No other conflicts declared.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The University of Limerick Faculty of Education and Health Sciences supported this research by providing SDH with a fee waiver for the academic years 2023–2024 and 2024–2025.
Ethical approval
The study was approved by the University of Limerick Faculty of Education and Health Sciences Research Ethics Committee on 13 December 2023 (study #2023_09_19_EHS).
Supplemental material
Supplemental material for this article is available online.
References
Supplementary Material
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