the influence of social networks and the broader environment

While many behavioural theories focus primarily on individual psychology, there are a range of theories which suggest that behaviour is influenced by others, including our perception of others, and/ or the broader environment, which are discussed in this section.

There is evidence that people do not consider all possible outcomes systematically when making many behavioural decisions (as is assumed in standard economic theory of rational choice). Instead, to cope with complex choices, people use heuristics which are strategies that enable faster decision making whilst only using some information (Gigerenzer et al., 2011; Kahneman, 2012). These heuristics have been shown to lead to predictable patterns of behaviour. Theory associated with ‘nudging’ (Thaler et al., 2008) – that is, ‘any aspect of the choice architecture that alters people’s behaviour in a predictable way without forbidding any options or significantly changing their economic incentives’ – has been extensively used to develop behaviour change interventions (Vlaev et al., 2016). Nudge theory focuses on automatic mechanisms (non-reflective decision making) and how the context can affect these in positive ways, although it does not exclude reflective mechanisms (deliberate, highly cognitive decision making). The mnemonic MINDSPACE (Messenger, Incentives, Norms, Defaults, Salience, Priming, Affect, Commitment and Ego) has been used to set out the most powerful contextual influences on automatic behaviours (Vlaev et al., 2016).

Social structure is about the patterns of social relationships within a population. An individual’s behaviour will impact upon these social relationships, and at the same time their social connections will affect their behaviour (Giddens, 1979). For example, a physically active person may join a running club and make friends with other runners, which might increase the amount the person runs. It has been suggested that friends and family influence weight-related behaviours and body weight (Zhang et al., 2018). People may influence each other through physical or online networks; for instance, social media is often used as a platform to influence behaviour (Hunter et al., 2019; Cascini et al., 2022). The interaction of many individuals within a social structure can alter that structure and change social norms. The theory associated with social structure (Giddens, 1979) is consistent with the theory of complex adaptive systems. Complex adaptive systems are made up of heterogeneous interacting elements and it is the relationships between these interacting elements which lead to potentially unexpected outcomes (Sterman, 2000). Public health interventions tend to operate within complex adaptive systems (Squires et al., 2016).

Social Norms Theory proposes that behaviour is influenced by perceptions of behavioural norms (Perkins et al., 1986). This may lead to the new behaviour becoming the social norm, thus changing the behaviour at the population level. Alternatively, social norms may make it harder for a new behaviour to diffuse and become the norm. It is therefore important to consider these interactions, rather than focusing solely upon the individual, to make more reasonable predictions.

Social Identity Theory proposes that each individual self-categorises based on their perceived membership of social groups (e.g., researcher, mother, runner) (Jetten et al., 2012). The extent to which they feel they share characteristics with other members will, in part, determine the influence of the group on their behaviours. The social connection to others affects health and wellbeing through these influences on behaviour, as well as directly through being able to count on social contacts (e.g., close connections in a running club may affect maintenance, frequency and length of exercise). These social connections are largely ignored when determining health-related outcomes within health economic models, yet their impact on mortality has been shown to be greater than obesity, blood pressure and physical inactivity (Holt-Lunstad et al., 2010). Social Identity Theory and the accompanying empirical evidence suggests that the focus on the individual to improve population health and wellbeing is insufficient (Jetten et al., 2012). In addition, the theory suggests that maintenance of healthy behaviour changes will be facilitated when an individual shifts from an identity for which the previous behavioural pattern was central to an alternative identity more supportive of the new behaviour (e.g., smoker to non-smoker) (Caldwell et al., 2018).

The life course approach recognises that over a lifetime, individuals accumulate health losses and benefits, and that at key forks in the life course, such as becoming pregnant or beginning work, these can be magnified and substantially impact future trajectories (Kelly et al., 2009). Thus, interventions may be more effective if they are targeted at specific stages of the life course. The life course approach recognises that by making changes to the environment and social norms, inequalities could be reduced, which may impact life course trajectories, and this could benefit the whole population and future generations (PHE, 2019).

Ecological frameworks have been developed which draw upon multiple theories to combine both individual and environmental influences for different health-related behaviours (Glanz et al., 2015). These frameworks recognise the interactions of influences across levels; however, they do not generally include quantifiable constructs. In public health it has long been recognised that interventions work best if they are provided at multiple levels: the individual, the community and the population (Dahlgren et al., 1991). This has been best demonstrated for smoking policy which has been highly successful during the past five decades (Glanz et al., 2015); for example, stop smoking services provided to individuals, training programs for practitioners at the community level and a ban in public places at the population level (McManus et al., 2018). It is important to consider the interaction between individual level factors and changes in the broader social and environmental context. The structure of the system is a key driver of its behaviour (Sterman, 2000; McManus et al., 2018).  We therefore need to be able to assess the potential impacts of changing the environment in addition to being able to assess individual-level interventions. Health economic modelling can provide a method for comparing and combining these interventions within one framework to explore their impacts, if the broader contexts that influence behaviour are incorporated within the models.