*1.2. Risk and Protective Factors for Psychological Outcomes During the Pandemic*

To date, studies on the psychological impact of COVID-19 have mainly focused on the role of sociodemographic variables (e.g., gender, age, education level, and social connections) in moderating reactions to the outbreak [10,11,24,35,36]. The identified sociodemographic risk factors for psychological distress include gender (female), age (18–30 or 60+ years old), student status, education level, perception of the public health system, specific physical symptoms (e.g., coryza, cough, sore throat, headache), and a low reported level of health [10,24,35]. For Chinese students, living in an urban area, having a

stable family income, living with parents, and having good social support were also found to protect against anxiety [11].

In addition to investigating sociodemographic factors, many studies have also outlined the role of certain dispositional traits in modulating responses to stressful events. However, these constructs have been poorly investigated in relation to the psychological impact of epidemics and, specifically, COVID-19. More generally, research has shown how individual differences, including dispositional traits, can explain life outcomes [37]. According to the theory of traits (or dispositional theory), individual differences may be explained by certain predispositions (traits), which are expressed in a relatively stable way across situations and time. Traits comprise a person's manner of thinking, feeling, perceiving, and relating to others [37]. Based on these considerations, dispositional traits might play a relevant role in predicting perceived stress in relation to COVID-19.

Coping is one of the most widely studied dispositional traits, and it has been found to be significant in modulating responses to stressful events. Coping is defined as the effort to solve personal and interpersonal problems in an attempt to master, minimize, or tolerate stress and conflict [38]. Distinct coping strategies have been found to be differentially associated with specific emotional responses [39], physiological stress responses [40], and self-efficacy [41,42]. One investigation into the role of coping strategies during a virus outbreak (2009 H1N1 flu pandemic) found coping style to influence the perceived risk of contagion and vaccination intentions among Canadian adults [43]. Another study, based in Singapore, found coping strategies to be associated with post-traumatic outcomes within visitors to community health care services during the national outbreak of SARS [23].

As regards emotional self-regulation and adaptation to the world, self-control may represent a significant protective factor. There is empirical evidence that people with high dispositional self-control have better psychological adjustment and impulse control [44]; this suggests that good self-control may mitigate the influence of a negative environment. Similarly, perceived control over life outcomes has been shown to be positively associated with well-being and health-related quality of life, and negatively associated with emotional distress, in the context of stressful events [45,46]. In this regard, locus of control [47] is a relevant concept, describing the degree to which an individual believes that they have control over the outcome of life events, as opposed to feeling that their life is subject to external forces beyond their control. Finally, among the many individual difference variables that might influence reactions to COVID-19, personality traits merit significant attention. Several studies have highlighted an association between the Big Five personality traits [48] and various health behaviors, such as sedentary behavior [49], sexual health behavior [50], physical activity [51], and alcohol consumption [52].

The first aim of the present study was to investigate the impact of the COVID-19 pandemic and the related government-imposed restrictions on perceived stress in a Western country (i.e., Italy). As reported above, most studies on the psychological impact of COVID-19 have related to the Chinese population. However, countries differ from one another in many important aspects (i.e., social, cultural, political, and economic aspects, to name only a few); consequently, psychological responses may also vary between contexts and communities, revealing unique qualitative and quantitative psychological reactions and psychological needs.

**Hypothesis 1 (H1).** *Our sample of Italian adults, collected during the COVID-19 outbreak, would show higher levels of perceived stress compared to Italian normative values.*

The second aim of the study was to confirm the role of certain sociodemographic factors in modulating stress responses to the COVID-19 pandemic, as reported in the recent literature.

**Hypothesis 2 (H2).** *(a) Participants who were female, younger, and students, with a lower level of education and lower income, would report higher levels of stress, and (b) participants who were living with others would report lower levels of psychological distress.*

The third aim of the work was to investigate the association between certain stable psychological traits and psychological distress relating to the current situation. To this end, participants were tested for coping strategies, self-control, locus of control, and select personality traits.

**Hypothesis 3 (H3).** *(a) Participants with positive coping strategies, higher levels of self-control, an internal locus of control, and higher levels of emotional stability would report lower levels of stress, and (b) participants with negative coping strategies, lower levels of self-control, an external locus of control, and lower levels of emotional stability would report higher levels of stress.*

Finally, with the goal of anticipating persons in need of treatment and improving the targeting and overall effectiveness of preventive programs, we aimed at developing machine learning models to predict individual psychological responses to the COVID-19 pandemic, based on sociodemographic and psychological variables with maximal sensitivity in classifying subjects with high versus low levels of perceived stress.

To summarize, the study was novel in the following two respects: first, it considered the role of not only sociodemographic variables, but also stable psychological traits, as predictors of a stressful reaction to COVID-19; and second, it leveraged machine learning techniques to identify people at the greatest risk of developing severe and negative psychological outcomes due to the pandemic.
