Introduction
The novel coronavirus disease 2019 (COVID-19) pandemic has emerged as a truly global public health crisis [1]. While symptoms of COVID-19 are relatively mild without serious consequences in the majority of cases [2], modeling data suggest that approximately 4% of the global population is at risk of severe COVID-19 if infected and may require hospital admission for treatment [3]. Furthermore, SARS-CoV-2, the virus that causes COVID-19, is highly contagious, spreading mainly through person-to-person contact. Government-mandated measures to reduce transmission include advocacy of behaviors like wearing face masks and social distancing and issuing “shelter-in-place” orders and bans on public gatherings [4].
Social distancing, defined as maintaining a distance of at least 3–6 feet (1–2 m) from other people not from the same household is considered particularly effective in minimizing SARS-CoV-2 transmission [5, 6]. “Shelter-in-place” orders (also referred to as “stay-at-home” or “lockdown” orders) represent means to mandate social distancing by minimizing incidences of person-to-person contact outside individuals’ immediate household. Similarly, bans on public gatherings seek to limit the frequency and number of people with whom they come into close contact. However, such actions do not eliminate all potential contact because individuals under such orders still need to break from shelter to fetch provisions and, for members of essential professions, to go to work. It is, therefore, imperative that individuals comply with public health guidelines advocating the practice of social distancing when they come into contact with others. Compliance with guidelines is also highly important in regions that have not issued formal “shelter-in-place” orders but have instead provided “safer-at-home” guidelines and in areas that have begun to lift “shelter-in-place” orders.
Public health organizations have been tasked with developing behavioral interventions that are efficacious in promoting social distancing behaviors among the general population [6]. Given that social distancing is a relatively novel behavior in many countries, identification of the determinants of social distancing behavior has become critical. Moreover, identifying determinants that are potentially modifiable through intervention, that is, can be targeted in messages or campaigns of behavioral interventions aimed at promoting social distance, is a recognized priority [7]. There have, therefore, been calls for research informed by behavioral science that identifies key determinants of preventive behaviors in the context of the current pandemic, particularly social distancing [7, 8]. However, there is relatively little research on the determinants of social distancing, particularly in the context of communicable disease prevention (e.g., influenza) in a global pandemic [9]. Previous research, for example, has tended to focus on the social cognition determinants of other preventive behaviors, such as facemask wearing [10], or focused on hypothetical scenarios [11] in the context of influenza prevention. To date, there are few studies informed by behavioral science on the individual determinants of social distancing in the context of the COVID-19 pandemic.
To fill this evidence gap, the current study aimed to identify the determinants of social distancing behavior among individuals subject to social distancing regulations during the COVID-19 pandemic. The research adopted an integrated theoretical approach based on social cognition theories to identify constructs that predict social distancing behavior and the processes involved. The research is expected to provide evidence of potentially modifiable targets for behavior change interventions aimed at promoting social distancing. Such interventions may contribute to reduced infection rates during the current pandemic and may assist in preventing a “second wave” of infections as “shelter-in-place” orders are lifted [5].

Social Distancing Determinants: An Integrated Social Cognition Approach
Research examining health behavior determinants has a long tradition of applying social cognition theories [12], which assume health behavior enactment is a reasoned process determined by beliefs, such as risk perception, attitude, social norm, and perceptions of control or self-efficacy. A prototypical social cognition approach is offered by the theory of planned behavior [13]. In the theory, individuals’ intention to perform the target behavior is proposed as the most proximal determinant of the performance of a future target behavior. Intention is a function of three constructs that summarize sets of beliefs regarding the future behavior: attitude (beliefs that the behavior will have advantageous or disadvantageous consequences), subjective norm (beliefs that significant others express support for performing the behavior), and perceived behavioral control (PBC; beliefs in the capacity to perform the behavior and to overcome barriers to the behavior). Intention is proposed to mediate the effects of attitude, subjective norm, and PBC on behavior. PBC is also proposed to predict behavior directly when it approximates actual control. Theory predictions have been supported in correlational and prospective research across multiple behaviors, contexts, and populations [14].
While the elegant parsimony of the theory of planned behavior is appealing, it is not without limitations. Research applying the theory has indicated that substantive variance in health behavior remains unexplained [14]. In addition, the size of the effect of intention on health behavior is often modest, suggesting a “shortfall” in those who report an intention to perform the behavior and those who act on their intention [15]. Researchers have, therefore, proposed modifications to the theory to resolve these limitations, such as integrating additional constructs from other theories, in the theory to predict behavior more effectively and address the intention–behavior “gap” [16].
Introducing additional constructs to the theory is one approach to increasing explained variance in health behavior. For example, researchers have examined relations between moral norms, an additional form of normative influence, and health behavior. Moral norms are considered particularly relevant when there is a moral imperative for acting (e.g., vaccination and blood donation) [17]. In the context of COVID-19, messaging from public health authorities on COVID-19-preventive behaviors has focused on protecting the vulnerable (e.g., immunosuppressed individuals, those with underlying health conditions, and the elderly) [3]. On this basis, we reasoned that moral norm would constitute a highly relevant determinant of social distancing intention and behavior in the context of the pandemic. In addition, anticipated regret has been shown to predict behaviors perceived likely to have adverse consequences or result in significant losses if not performed [17]. Failure to perform social distancing behaviors may be perceived as having highly undesirable consequences, such as becoming infected or infecting vulnerable others. We, therefore, included moral norm and anticipated regret as additional predictors of intention to perform social distancing behavior in our integrated model.
Researchers have applied “dual-phase” models as a means to resolve the limitation of the intention–behavior “gap.” Models like the model of action phases [18] and the health action process approach (HAPA) [19] propose that individuals need to augment their intentions with action plans in order to enact them. Action plans reflect the extent to which individuals have specified when, where, and how they will perform the intended behavior. The model of action phases [18] suggests that individuals will more likely enact their intentions if they form an action plan, so action plans are proposed to moderate the intention–behavior relationship. By contrast, the HAPA suggests that planning is part of the process of intention enactment such that action plans mediate the intention–behavior relationship [19]. Meta-analyses of studies in health behavior have supported both processes [20, 21], and we aimed to test both in our proposed integrated model of social distancing behavior.
While social cognition theories like the theory of planned behavior assume participation in health behavior to be a reasoned process, research applying such theories has shown that past behavior remains a pervasive determinant of behavior alongside the theory constructs [22, 23]. The inclusion of past behavior as an independent behavioral predictor in a social cognition theory is important because it provides a test of its sufficiency in accounting for unique variance in behavior. However, residual effects of past behavior on behavior are also assumed to model the effects of other unmeasured constructs on behavior [23]. One candidate construct is habit, which reflects the “nonconscious” or “automatic” enactment of a behavior developed through its repeated performance in stable contexts [24, 25]. Research examining the effects of habit in the context of social cognition theories has examined how self-reports of experiencing the behavior as “automatic” and “unthinking” predict health behavior independent of intentions [26]. The introduction of habit in our augmented model, therefore, may provide important information on the extent to which social distancing behavior is determined by reasoned or nonconscious processes [27].

The Present Study
The present study aimed to identify the determinants of participation in social distancing behavior among individuals in the context of COVID-19 using an integrated social cognition model that incorporated constructs from the theory of planned behavior with moral norm, anticipated regret, action planning, and self-reported habit. We tested predictions of the proposed model in a prospective correlational study in two separate samples of adults from Australia and the USA, respectively. These countries provide an opportunity to examine the determinants of social distancing because they experienced rapid increases in COVID-19 cases relatively early in the pandemic and introduced public health advice and “lockdown” measures to minimize transmission via social distancing. In our proposed model (Model 1; Fig. 1), attitude, subjective norm, PBC, moral norm, and anticipated regret were specified as predictors of intention, and intention, PBC, and habit as predictors of social distancing behavior. Intention was proposed to mediate the effects of the social cognition constructs on behavior. The role of action planning as a mediator and moderator of the intention–behavior relationship was also specified. We also specified a second model (Model 2; Fig. 1) in which past social distancing behavior was included as a direct predictor of all constructs in the model, providing a test of its sufficiency. Although research demonstrating that social distancing behavior clusters with other health behaviors indicates that application of social cognition theories is viable for this behavior [28], research is needed to verify this contention and the current study contributes to this goal. The research may assist in identifying potentially modifiable constructs that relate to social distancing behavior. Such information may provide useful information to inform social distancing interventions focused on reducing the spread of COVID-19 and, more broadly, other communicable diseases.
Fig. 1.  Standardized parameter estimates of the integrated model. Upper panel presents the model excluding past behavior (Model 1) and the lower panel presents the model including past behavior (Model 2). Coefficients printed on the upper line are for the Australian sample and coefficients printed on the lower line are for the U.S. sample. †Effect is significantly different across the Australian and U.S. samples in multiple-group analyses. *p < .05, **p < .01, ***p < .001.