The Synergistic Change Model (SCM) is based in complex dynamics systems theory (Thelen, 2005) and emphasises the complex interplay of dynamic elements that facilitate lasting positive change in functioning. These elements comprise of five psycho-social ' Domains of Positive Functioning'
(Rusk and Waters, 2014), including: attention and awareness, comprehension and coping, emotions, goals and habits, and relationships and virtues; further to environmental and biological/physiological influences (Rickard & Vella-Brodrick, 2014). The SCM suggests that whilst each of the psycho-social domains operate independently (Rusk & Waters, 2015), each element may also interact and influence functioning in all other domains; working to either reinforce or undermine change.
According to the SCM, interventions may result in one of three processes of change: relapse, spill-over, and synergy. ‘Relapse’ may occur when changes in one domain are inadequate, unstable, and made to one of two domains in isolation. Isolated changes are less likely to change the overall dynamic stability of the psycho-social system and instead results in between-domain interactions which undermine and prohibit initiated change within a given domain. Thus, individuals revert to their original state of undesired functioning. In contrast, spill-over occurs when the effects of positive change in one domain "spill over" to enhance functioning in other domains. Spill over effects from enhancements in one domain on to another are often reported in qualitative investigations of patient experiences (Landsman-Dijkstra, van Wijck, & Groothoff, 2006) and may be evidenced as mediation effects within the literature (Toussaint & Friedman, 2009). Spill-over effects demonstrate that cognitive functions do not operate independently and offer insight as to how different interventions may result in similar changes being accomplished through multiple pathways of pursuit (Oman, Richards, Hedberg, & Thoresen, 2008). However, these residual effects are often temporary and offer no promise of sustainable change. To induce enduring change, mutually supportive and reinforcing changes must occur within several domains of psycho-social functioning. These synergystic interactions result in a new dynamically stable pattern of behaviour; typically referred to as upward positive spirals (Ryff & Singer, 1998; Crawford & Caltabiano, 2011; Gudan, 2010; Lyubomirsky & Layous, 2013; Wood, Maltby, Gillett, Linley, & Joseph, 2008) and identified as mechanisms through which interventions may enhance well-being (Cohn & Fredrickson, 2010). According to the SCM, the formation of these synergistic spirals is a powerful means by which the effect of an intervention can be made enduring; and that interventions will be more effective if they are designed to produce synergistic change.
Considering features central to sustained positive change, \citealp{Rusk_2017} highlight several strategies that can be adopted to facilitate interventions; including targeting pivotal domains, leveraging existing strength’s and values, and targeting mutually reinforcing elements. Briefly, pivotal elements are those domains that can initiate synergistic changes that ‘tip the system into a new stable mode of functioning’ (Rusk et al., 2017). For example, positive emotions are considered pivotal elements that create ‘upward spirals’ that broaden thought-action repertoires, build psychological and social resources and foster positive emotions futher (Fredrickson & Joiner, 2002; Fredrickson, 2004; Garland et al., 2010). Consequently, interventions that cultivate positive emotions may trigger synergistic changes within a range of psycho-social domains that enhance and sustain benefits to well-being. Further to this, intervention strategies should be tailored to an individual’s traits, values or character strength’s profile; leveraging these to support the desired change through synergistic interactions. Lastly, the SCM (Rusk et al., 2017) suggests that change within a given domain of psycho-social functioning, particularly non-pivotal domains that lack synergistic potency, will be more successful if mutually reinforcing domains are targeted to foster synergistic change and stabilise functioning. Moreover, the SCM suggests that targeting elements of psycho-social functioning from the behaviour change literature (e.g. implementation intentions, self-efficacy) in addition to elements from, for instance, the positive psychology literature (e.g. gratitude, optimism, or mindfulness) may further induce enduring change. Thus, the SCM holds the potential to integrate the knowledge captured within existing behavioural change theories to bear in creating positive psychological change.