Ingo Zettler’s research while affiliated with IT University of Copenhagen and other places

Study participants are vital to personality research. Thus, individuals not following study invitations (self-selection), not completing all administered measures (showing dropout) and/or not participating at subsequent measurement occasions (showing attrition) pose a significant challenge to personality research. Building on existing research documenting that non-response does not occur randomly, we herein test for potential predictors of non-responding at each of the three stages by combining official register (census) data from a randomly selected participant pool of 100,175 adults, representative for the target population (adults living in Denmark), with data from a personality panel (N = 14,071) recruited from this participant pool. We find that each socio-demographic characteristic considered (i.e., sex, age, marital status, migration background, income, highest completed education, and region of residence) as well as five of the six HEXACO personality dimensions (Honesty-Humility, Emotionality, Extraversion, Conscientiousness, and Openness to Experience; but not Agreeableness vs. Anger) were associated with self-selection, selective dropout, and/or selective attrition. We further compare the sample representativeness at each of the stages and illustrate how to assess potential biases (regarding the obtained HEXACO scores) due to self-selection.

Study participants are vital to personality research. Thus, individuals not following study invitations (self-selection), not completing all administered measures (showing dropout) and/or not participating at subsequent measurement occasions (showing attrition) pose a significant challenge to personality research. Building on existing research documenting that non-response does not occur randomly, we herein test for potential predictors of non-responding at each of the three stages by combining official register (census) data from a randomly selected participant pool of 100,175 adults, representative for the target population (adults living in Denmark), with data from a personality panel ( N = 14,071) recruited from this participant pool. We find that each socio-demographic characteristic considered (i.e., sex, age, marital status, migration background, income, highest completed education, and region of residence) as well as five of the six HEXACO personality dimensions (Honesty-Humility, Emotionality, Extraversion, Conscientiousness, and Openness to Experience; but not Agreeableness vs. Anger) were associated with self-selection, selective dropout, and/or selective attrition. We further compare the sample representativeness at each of the stages and illustrate how to assess potential biases (regarding the obtained HEXACO scores) due to self-selection.

Previous research has shown that parents' vaccination readiness, as measured by the 7C vaccination readiness scale, helps to understand whether and why parents are (not) willing to vaccinate their children. However, there is a lack of research investigating the association between parents' vaccination readiness and their children's actual vaccine uptake. Addressing this gap, we examined how Danish parents' level of vaccination readiness is associated with their child's vaccination status combining survey with official registry data. Specifically, parents residing in Denmark (N = 2941, 64 % female) completed a survey assessing their level of vaccination readiness with the 7C vaccination readiness scale for parents, trust in different sources of information on vaccination, and certainty about vaccinating their child with the next vaccine in the program. Additionally, official vaccination registry data on various recommended child vaccinations was obtained and matched to the survey data of their parents. Results from logistic regression analyses indicate that parents' readiness to vaccinate their children was substantially associated with completion of children's vaccination doses. More precisely, a one-point increase in parents' vaccination readiness score was associated with a two-fold increase in the likelihood of the child being vaccinated with the three main vaccines in the program. The results also show associations between each of the 7C factors, trust items, and demographic variables with real behavior as well as parents' certainty to vaccinate their children in the future. The findings further substantiate the usefulness of assessing parental vaccination readiness, with potential implications for intervention planning by researchers and policymakers.

Honesty, defined as freedom from fraud or deception, is widely valued in many aspects of life, from personal relationships to professional settings. Yet acts of dishonesty remain widespread, including political and corporate scandals, misinformation, personal betrayal, and so on. Understanding honesty and the factors that influence it provides insights that are essential for fostering trust and combating corruption. In this review, we synthesize key findings from research on honesty, focusing on when people choose to be truthful or deceptive. We argue that although much is known about honesty in isolated, low-risk contexts, an urgent need exists to study honesty in more complex, realistic settings, such as those involving interpersonal relationships, potential sanctions, or group influences. Our proposed framework highlights understudied contexts and encourages future studies to explore settings where enforcement and social dynamics play a significant role in decision-making. To do so, we point out 66 open research questions that we find most promising to explore. By integrating insights from multiple disciplines, we aim to advance the understanding of honesty and provide a roadmap for research that can inform policies and interventions to promote integrity in society.

Crime is an issue with severe consequences for individuals, economies, and society at large. Developing effective crime prevention strategies requires a clear understanding of who is likely to engage in crime and why. A promising approach in this regard likely is integrating established criminological theories with established models of basic personality structure. Correspondingly, the present investigation derives hypotheses from three criminological theories—self-control theory/general theory of crime, situational action theory, and general strain theory—on the relation between the HEXACO personality dimensions and crime. The preregistered hypotheses were tested by linking HEXACO data of a Danish adult personality panel (N = 12,496) to official records on all criminal convictions of the participants registered within the past 41 years. Results revealed negative associations of honesty–humility, emotionality, agreeableness versus anger, and conscientiousness with crime (0.71 ≤ odds ratios ≤ 0.88). Except for agreeableness, effects were robust to controlling for relevant background variables (e.g., sex, age, education, income). The relation of the HEXACO dimensions varied only slightly across different types of offenses (e.g., interpersonal crimes, property crimes). In sum, this investigation provides a robust theoretical and empirical basis for how personality relates to crime.

People regularly encounter situations in which they have to engage in tasks they find boring or irrelevant, in which case their autonomy—the need to act in ways that are meaningful for oneself—is impeded. When there is no motivational support available, individuals need to find ways to overcome their motivational barriers by themselves. Applying autonomy-regulation strategies may be effective for increasing autonomy and particularly the more adaptive types of motivation (i.e., intrinsic and internalized). Testing this idea, we investigated whether individuals apply self-supportive strategies to boost their feelings of autonomy and motivation in two studies via cross-sectional survey samples (overall N = 2,344). We analyzed how autonomy regulation strategies were associated with theoretically related variables via Structural Equation Modeling (SEM). In Study 1, the self-reported use of autonomy regulation strategies was strongly positively associated with intrinsic and internalized types of motivation, weakly positively correlated with introjected avoidance motivation, and not associated with external motivation. In Study 2, we introduced two dilemmas concerning motivational problems individuals face when engaging in tasks and being assigned a task, respectively. Results indicate that individuals report using general strategies of autonomy regulation to achieve fulfillment of autonomy and intrinsic motivation, next to more specific autonomy regulation strategies regarding specific dilemmas. Our results show that it would be worthwhile to investigate if stimulating individuals to use autonomy regulation strategies would positively affect their motivation (e.g., in job or study contexts), and that in doing so, it is important to consider both specific context effects on autonomy regulation as well as individual preferences for general strategies used to regulate one’s autonomy.

What were relevant predictors of individuals' proclivity to adhere to recommended health‐protective behaviors during the COVID‐19 pandemic in Denmark? Applying machine learning (namely, lasso regression) to a repeated cross‐sectional survey spanning 10 months comprising 25 variables (Study 1; N = 15,062), we found empathy toward those most vulnerable to COVID‐19, knowledge about how to protect oneself from getting infected, and perceived moral costs of nonadherence to be strong predictors of individuals' self‐reported adherence to recommended health‐protective behaviors. We further explored the relations between these three factors and individuals' self‐reported proclivity for adherence to recommended health‐protective behaviors as they unfold between and within individuals over time in a second study, a Danish panel study comprising eight measurement occasions spanning eight months ( N = 441). Results of this study suggest that the relations largely occurred at the trait‐like interindividual level, as opposed to at the state‐like intraindividual level. Together, the findings provide insights into what were relevant predictors for individuals' overall level of adherence to recommended health‐protective behaviors (in Denmark) as well as how these predictors might (not) be leveraged to promote public adherence in future epidemics or pandemics.

Motivated by theoretical accounts positing that participation in intergroup conflict is driven by a desire to promote the in-group, past studies have explored the link between prosocial personality dimensions and out-group harm. However, while dimensions such as Honesty-Humility predict in-group cooperation, they do not explain out-group harm. Across two incentivized experimental studies (one preregistered; overall N = 1,584), we show that out-group harm is uniquely associated with higher levels of the Dark Factor of Personality (D), a personality dimension capturing the core of all aversive personality characteristics. Conversely, high levels of D, alongside low levels of Honesty-Humility, are associated with less in-group cooperation. Our results show that in-group cooperation and out-group harm are associated with distinct personality dimensions.