The recruitment of the participants took place in the framework of the nationally-representative CON-VINCE study, aiming at evaluating the dynamics of the spread of the COVID-19 disease as well as getting insights into the mental health of the Luxembourgish population (31). The chosen sampling strategy for the representativeness of the Luxembourgish population was based on gender-, age-, and residency-stratification in collaboration with a specialized survey company (TNS-ILRES) (31).

The full study has been described in detail elsewhere (31). The online administered questionnaire consisted, among others, of socioeconomic and health indicators, and validated scales to assess depression, anxiety, loneliness, stress, and personality traits.

Given the multilingual characteristic of Luxembourg, we used questionnaires with translations to all the four languages (German, French, English, and Portuguese) (32–34) and applied in large multi-country surveys such as the Survey of Health, Aging and Retirement in Europe (35, 36). This was done to ensure that participants could choose their preferred language to answer the study questionnaires.

The study was approved by the national research ethics committee (Comité National d'Ethique de Recherche, CNER), under reference 202004/01, and by the Luxembourgish Ministry of Health under reference 831x6ce0d. Furthermore, the study has been submitted for registration on ClinicalTrials.gov (NCT04379297).

A total of 1,828 participants were randomly selected based on three stratification variables (gender, electoral district, and age) in order to reach representativeness of the Luxembourgish population (18–79 years).

The study data were managed by using the ADA: the CON-VINCE Discovery Platform. STATA version 16 (StataCorp LP, College Station, TX, USA) was used to conduct statistical analyses, with α levels set at 0.05. Firstly, we computed descriptive statistics for demographic and socioeconomic variables, as well as psychological outcomes stratified by age groups.

Secondly, bivariate correlations were calculated to assess the associations between the independent variables and the continuous mental health outcomes (depressive symptoms, loneliness, anxiety, and stress). Finally, we performed multivariate regression models. We report unstandardized beta regression coefficients that indicate the change in the dependent variable for a one-unit increase in the independent variable. In the first set of regressions, we explored the associations of personality traits with the four mental health outcomes in separate models, controlling for sociodemographic variables. To check that the associations of psychological scales results with personality traits remained significant after adjustment, we introduced one variable at a time in the regression model before estimating the complete model. In a second step, health and social behaviors were additionally included to test if they could explain the relationship between personality traits and mental health outcomes. In a separate set of analyses, resilience was added as a main term and as an interaction term with the personality traits, first one at a time. Since associations did not change when entering all personality traits and their interaction terms with resilience at once, only the model incorporating all interactions is presented. Another way to conceptualize resilience is to hypothesize it as a mediator in the personality-mental health relationship. Therefore, in a last step, a structural equation model was set up to test the mediating role of resilience, using maximum likelihood method, as recommend by previous literature (54), the model fitted the structural equation modeling criteria (root mean square error of approximation—RMSEA and standardized root mean square residual—SRMR <0.08, goodness of fit index—GFI and comparative fit index—CFI >0.90).

After excluding 34 participants with missing values on sociodemographic and other variables of interest, data of a total of 1,828 participants were analyzed (51.1% women). Participants' mean age was 47.6 years (SD = 15.1), average number of schooling was 14.0 years (SD = 3.7). The majority of participants (65.1%) were married or living in a registered partnership. More than half of the participants lived in their own house (73.7%), except for people in their 30s (39%). Most of the participants were Luxembourgish nationals (85.2%, Table 1).

Regarding psychological variables, 687 participants (37.7%) indicated a high level of stress, and 114 participants (6.2%) displayed moderate anxiety levels. Significant levels of moderate and higher depression as well as loneliness were found in 384 (21%) and 383 (20.9%) participants, respectively. Thousand four hundred and forty-six participants (79%) had typical levels of resilience, while 346 (18.9%) reported low resilience levels. In the age range 18–29, more people scored above the cut-off for moderate depression (36.4%), anxiety (12.0%), and loneliness (30.6%) than the other age groups. In the same age range, participants reported higher levels of stress (48.8%) than in the other age ranges. The prevalence of moderate levels of psychological distress was stable across the age ranges.

Frequency of physical activity significantly decreased during the confinement compared to before the pandemic (63.7 vs. 54.2%; p < 0.001) in all age groups. However, the time spent on physical activity significantly increased during the pandemic for all the age ranges (p < 0.001). Moreover, young adults (18–29 years) spent more hours per day on the internet (M = 3.5, SD = 3.0), on social media (M = 3.4, SD = 3.7), on the phone (M = 2.1, SD = 2.6), and on streaming platforms (M = 3.5; SD = 3.8) compared to the other age groups. In the other age ranges, mean hours spent on technical devices remained stable (Table 1). Additional analyses showed no associations between annual income brackets and mental health outcomes.

As we expected, anxiety was positively correlated with depressive symptoms (r = 0.79, p < 0.001), stress (r = 0.16, p < 0.001) as well as with loneliness (r = 0.44, p < 0.001). Depressive symptoms were positively correlated with loneliness (r = 0.52, p < 0.001), and with stress (r = 0.76, p = 0.001).

We found positive correlations between agreeableness and resilience (r = 0.14, p < 0.001) as well as between conscientiousness and resilience and between extraversion and resilience (r = 0.78, p = 0.001, and r = 0.98, p < 0.001, respectively). A negative correlation has been established between resilience and neuroticism (r = −0.28, p < 0.001).

In the first set of analyses, depression, anxiety, loneliness, and stress served as dependent variables, and we controlled for age, gender, education, marital status, and type of housing.

Here, higher agreeableness was associated with lower depression (B = −0.58; SE = 0.25), lower anxiety (B = −0.28; SE = 0.10), lower loneliness (B = −0.15; SE = 0.05), and lower stress (B = −0.41; SE = 0.09; Table 2). Higher conscientiousness was also associated with lower depression (B = −0.97; SE = 0.24), lower loneliness (B = −0.13; SE = 0.04), and lower stress (B = −0.32; SE = 0.08). Low extraversion predicted higher stress (B = −0.22; SE = 0.67). Conversely, high neuroticism was associated with higher depression (B = 3.39; SE = 0.20), higher anxiety (B = 1.72; SE = 0.09), higher loneliness (B = 0.34; SE = 0.04), and higher stress (B = 1.05; SE = 0.71). Higher openness was associated with higher depression (B = 0.57; SE = 0.19), higher anxiety (B = 0.28; SE = 0.08), and higher loneliness (B = 0.08; SE = 0.03; Table 2). Respondents with more years of education had less anxiety (B = −0.05; SE = 0.02). Participants living in a house showed fewer depression symptoms than those living in an apartment (B = −1.58; SE = 0.40). Furthermore, marital status played a role: higher stress symptoms were found in respondents who reported being single (B = 0.43; SE = 0.19) or widowed (B = 1.01; SE = 0.40), while higher loneliness symptoms were associated with being single (B = 0.40; SE = 0.09), divorced (B = 0.39; SE = 0.11), or widowed (B = 0.45; SE = 0.20). The percentage of variance (R²) explained by the independent variables in the models for stress, depression, anxiety, and loneliness scales were 23, 27, 29, and 14%, respectively.

By further including health and social behaviors in the second set of analyses, we found that the more time people spent on social media, the more they experienced depression (B = 0.19; SE = 0.08), anxiety (B = 0.08; SE = 0.04), loneliness (B = 0.03; SE = 0.02), and stress (B = 0.07; SE = 0.03; Table 3). Other social and health behaviors were not significantly associated with the mental health outcomes and did not modify the personality-mental health relationships. The independent variables explained a total of 24% percentage of variance in the model for stress, 28% in the model for depression, 30% for anxiety, and 14% for loneliness.

In the next step, the models additionally included resilience, which was strongly and negatively associated with all four mental health outcomes (Table 4). Including resilience, the direction and significance of associations of stress, anxiety, and loneliness with personality traits did not change. Depression, agreeableness, and extraversion were no longer significantly associated with resilience, suggesting that resilience was more strongly associated with mental health than the personality traits. The independent variables explained 24% in the model for stress, 30% in the model for depression, 31% in the model for anxiety, and 15% for loneliness.

Next, testing the moderating role of resilience on mental health outcomes, resilience was interacted with the personality traits first one at a time, then in a joint model. As the associations were similar, only the full model containing all five interactions is reported (Table 5). Here, in more conscientious respondents, higher resilience was associated with higher levels of stress (B = 0.316, SE = 0.148, p = 0.033). In more neurotic respondents, higher resilience was associated with lower levels of stress (B = −0.259, SE = 0.124, p = 0.037). Higher resilience was also associated with lower levels of depression and anxiety, respectively, in more neurotic respondents (depression: B = −1.798, SE = 0.349, p = 0.000; anxiety: B = −0.989, SE = 0.147, p = 0.000). Finally, in more open respondents, higher resilience was associated with lower levels of depression and anxiety (depression: B = −1.175, SE = 0.344, p = 0.001; anxiety: B = −0.431, SE = 0.145, p = 0.003).

In a last step, a structural equation model mediation analysis was carried out to test whether the resilience could explain the associations between personality traits and mental health during the pandemic, also controlling for sociodemographic variables. The results showed that resilience plays a role as a mediator in mental health outcomes. More specifically, higher levels of resilience in more extroverted people were associated with higher levels of perceived stress (B = 0.355; SE = 0.058; p < 0.01), whereas they are associated with lower levels of anxiety (B = −0.089; SE = 0.037, p < 0.05), depression (B = −0.097; SE = 0.036, p < 0.01), and loneliness (B = −0.013; SE = 0.005, p < 0.05). Similarly, more resilient, and conscientious people showed higher levels of perceived stress (B = 0.025; SE = 0.010, p < 0.05), loneliness (B = 0.134; SE = 0.023, p < 0.01), and they tend to have lower levels of anxiety (B = −0.048; SE = 0.018, p < 0.01). Table 6 shows the indirect effects of the model, and Figure 1 shows the model tested.

The aim of this study was to investigate the associations between personality traits and mental health in a period of confinement during the first wave of the COVID-19 pandemic in a nationally representative sample, and to which extent social and health behaviors would explain the personality-mental health relationships. We further explored the moderating role of resilience in the personality-mental health relationship.

The CON-VINCE participants reported higher levels of moderate depression compared to another study in Luxembourg carried out before the pandemic (55) and comparatively high levels of loneliness. The prevalence of depressive symptoms during the pandemic was in line with previous findings (10). Comparing the findings to another European country, Luxembourg, at that time point, only had few confirmed COVID-19 cases and a low prevalence of the SARS-CoV-2 virus (31), and had comparatively lower anxiety levels than Austria at the same time (56).

Confirming earlier findings (11), higher levels of education were associated with fewer depression symptoms. Higher education seems to be related to greater stability and access to employment opportunities, which is associated with higher well-being, on the other hand, people with lower education are the ones that might experience the first impact of the economic crisis due to restriction measures (57). As reported in other countries, such as Italy (14) and France (58) we also found that the type of housing was associated with mental health, with respondents living in an apartment reporting increased depression symptoms. This may be due to feeling more confined when living in a (usually less spacious) apartment. However, as living in a house is a robust proxy for wealth in this setting, also more robust than annual income for which we did not find associations with mental health, these findings may also point to socioeconomic inequalities in mental health.

Younger respondents presented higher scores on depression and anxiety scales as well as higher feelings of loneliness and perceived stress than other age groups in the CON-VINCE study (12) in line with earlier studies (3, 16). Testing the association of personality with mental health, personality traits were associated with mental health outcomes independent of age and other socio-demographic confounders.

The positive correlations between resilience and personality traits showed that the higher the participants scored on the traits agreeableness, conscientiousness, and extroversion, the higher their resilience was. The negative correlation between resilience and neuroticism showed that more neurotic participants were less resilient.

We found associations between neuroticism and impaired mental health such as depression, anxiety, loneliness, and stress, in line with findings from pre-pandemic studies (5, 59). Neuroticism has been found to be linked to negative affect in a German sample in the first wave of the pandemic (60). Resilience was negatively linked to neuroticism, confirming previous results of neuroticism being a risk factor for anxiety and depressive symptoms (61, 62).

While conscientious people would search for distractions or act to resolve their problems, respondents with higher scores of neuroticism may ruminate as a way to react to stressful events, which may increase vigilance for possible threats in turn associated with stress and anxiety symptoms (63). In addition, if anxiety symptoms are not treated, it can potentially increase depression levels by the intense ruminating on negative expectations and persistent worries (64). In contrast to the literature, we found that people with higher levels of openness experienced higher levels of depression, anxiety, and loneliness. However, this result could be explained by different facets of this personality trait, especially fantasy, which may lead to experiencing higher discrepancies between idealized and actual self- or world-states and come with a higher risk for depression (65). We found that people scoring high in conscientiousness are experiencing lower stress levels inconsistent with pre-pandemic studies (66, 67), suggesting that higher conscientiousness may be beneficial in adjusting to pandemic control measures and accepting the new situation.

We found respondents with higher levels of extraversion to be experiencing lower levels of stress, in line with previous findings (68). Participants scoring lower on agreeableness were experiencing higher stress levels, again confirming previous findings (69). Interestingly, we could confirm a protective role of agreeableness and extraversion on perceived stress, personality traits which may have helped to activate beneficial coping strategies as suggested earlier (11). However, in this study, extraversion was not associated with lower anxiety (10), pointing to a more important role of agreeableness.

The social and health behaviors investigated in this study, specifically the daily time spent on the internet, news, and TV, phone calls as well as on streaming platforms and by the physical activity before and during the pandemic unexpectedly had limited value to explain levels of stress, depression, anxiety, and loneliness, except time spent on social media. Further, the investigated social and health behaviors did not substantially change the personality-mental health relationships. One possible explanation is that the items to assess time spent with different behaviors may not have been able to capture fine-grained differences in the behaviors, or that behaviors resulted from different motivations or took place in different contexts (e.g., streaming alone vs. as a family or couple activity).

We found more time spent on social media to be related with stress, depression, anxiety, and loneliness, but not with personality traits. Our results provide insight into the negative role of social media in mental health, and confirm earlier findings (26) in the pandemic context. Due to the cross-sectional nature of our study, there is, however, the possibility of reverse causality. We believe that different problematic contents in social media, such as fake news and conspiracy theories, or overly positive self-portrayals of others, could lead to increased levels of stress and anxiety. We also believe that social media may provide reminders of social contacts, foreign places, and activities that were missed or not possible to reach during the confinement. This could have led to increased depressive symptoms and feelings of loneliness.

We found that higher resilience was associated with lower levels of depression, stress, anxiety, and loneliness, in line with previous research (70). Additional analyses showed that resilience moderated some of the personality-mental health associations, most consistently by lowering the negative associations of neuroticism with stress, depression, and anxiety in persons with higher resilience. Additionally, testing a potentially mediating role of resilience in the personality-mental health relationship with structural equation modeling confirmed the findings from the multivariate regression analyses. Due to the cross-sectional nature of the study, the potentially causal mediating role of resilience cannot be established and stricter research designs are needed to arrive at robust conclusions about the moderating vs. mediating role of resilience. However, the results point to an important contribution of resilience in mental health during the first wave of the COVID-19 pandemic. Considering that resilience has been shown to be modifiable through interventions (30), people with higher neuroticism may benefit from resilience interventions to improve coping strategies and reduce symptoms. Further, higher conscientiousness was associated with higher levels of stress in persons with higher resilience. A possible explanation could be that high levels of conscientiousness and high levels of resilience could be associated with a strong sense of having control over one's circumstances, which could go along with feelings of having to prepare or execute precautions not to lose control, which could, in turn, be associated with higher levels of stress.

Strength of the study was a population-representative sample with a rapid data collection during the height of pandemic control measures in April 2020. As a limitation, we could not account objective self-isolation in the personality-mental health relationship as some participants were still commuting to work whereas others were staying at home, with possibly limited social exchange. Other factors such as asymptomatic COVID-19 infection or COVID-19 disease of the respondents or their loved ones were not included in the analyses; however, at this time prevalence of the SARS-CoV-2 virus was very low in Luxembourg (31).

The multilingual sample necessitated the use of a total of four languages. Psychometric testing of the scales was not possible in language-stratified subsamples as the sample sizes by language were too small. Not all scales have been validated in all four languages in previous studies, however, checks with several multilingual colleagues and back translation were undertaken to ensure proper translation. The multilingual assessment may have resulted in diminished internal consistencies of the scales.

Additionally, we did not have information on mental health status of the CON-VINCE participants before the pandemic. The prevalence of depressive disorders has risen sharply in the last years in Luxembourg, already before the pandemic. In 2017, 5.0% of the Luxembourgish population showed elevated levels of depressive symptoms (71), whereas in 2019, this number had already doubled (72). Elevated levels of negative psychological outcomes may thus be due to ongoing developments in the country, for instance, rising housing prices and increasing inequality (17). The CON-VINCE study sample is representative in terms of gender and age of Luxembourg residents, however migrants, which constitute a large share of the residents, may not be well-represented (73).

Findings on higher depression levels during the pandemic control measures underline the need for psychological support during times of a pandemic. Additionally, in psychological interventions or psychotherapy, knowledge about the personality structure of trainees or clients could potentially benefit efforts to increase mental health during pandemic control measures.

Resilience, as shown in recent literature, is not only shaped by the individual, but originates from other factors such as family, community, and culture (74). Wang and Morav (75) showed that civic participation or living in a neighborhood with strong community support and friendship may also help build strong resilience. In this context, a recent study showed that the feeling of neighborhood attachment differs within ethnic minorities and that this feeling is more pronounced for the second-generation minorities (76). As Luxembourg is composed of almost 50% foreigners (77), public policies should also pay more attention to promote interethnic dialogues and residential integration in order to strengthen resilience throughout the community.