Psychometric properties of the Adverse Childhood Experiences Questionnaire 10 item version (ACE-10) among Hungarian adolescents

Psychometric properties of expanded adverse childhood experiences assessment questionnaire at a wellness centre in India

The original Adverse Childhood Experiences (ACEs) assessment questionnaire with 10 items has been extensively used to assess and identify associations with long-term negative outcomes in mental health, physical health, and behaviour globally. The past three decades of research has also identified a few additional categories of ACEs beyond the original ten questions. However, there is a gap in the Indian context to establish the psychometric properties of the expanded ACE Assessment Questionnaire and explore associations with mental health parameters.

OBJECTIVE

This study evaluated the psychometric properties of an expanded ACE Assessment Questionnaire at a wellness centre in India, incorporating culturally relevant modifications to the original 10 items.

METHOD

An additional six questions (Dangerous neighbourhood, Loss of parent or guardian, Peer bullying or victimization, Peer isolation or rejection, financial difficulty, and Parental fights) based on decades of evidence since the original 10-item questionnaire were added. Internal validity, internal consistency using McDonald's Omega and item-total correlation followed by principal component analysis were carried out, and confirmatory factor analysis was used to validate the factor structure and model fit indices. Questions which did not contribute to the construct were removed and predictive analysis was conducted using linear regression to predict depression and anxiety using the expanded questionnaire.

RESULT

Two questions (incarceration in the family from the original 10-items questionnaire and loss of parent or guardian from the additional six questions) were removed since they did not contribute significantly to the psychometric properties. The results of the remaining 14-item questionnaire confirm that it is reliable (McDonald's Omega) and meets content validity criteria based on three-factor structure (Factor 1 - Childhood Maltreatment, Factor 2 - Resource Scarcity & Environmental Distress, Factor 3 - Household Challenges).

CONCLUSION

The findings highlight that additional questions are relevant in the Indian context, and the revised 14-item questionnaire has better psychometric properties while maintaining its conceptual scope in that context. The findings validate these modifications in larger, representative Indian samples to ensure the questionnaire's reliability in assessing childhood adversity and its association with long-term effects.

Abnormal interbrain coupling in individuals with childhood adversity may underlie their difficulties in benefiting from social interactions

BACKGROUND

While adverse childhood experiences (ACEs) such as abuse or neglect are linked to lifelong interpersonal challenges, it's uncertain whether individuals with ACEs can effectively draw on others for distress relief and whether neural dyadic processes in these exchanges are compromised.

METHOD

To address this gap, here we examined interbrain coupling between 'targets' (adults with a varying history of ACEs) and 'regulators' (unacquainted individuals without a history of ACEs) during two conditions: (i) distressing condition: where the target shares with the regulator a distressing biographical event; (ii) neutral condition: where the target shares with the regulator a neutral biographical event. After screening 534 participants, 58 dyads were simultaneously scanned with functional near-infrared spectroscopy (fNIRS), during the distress/neutral conditions to investigate interbrain coupling in the dorsolateral pre-frontal cortex (DLPFC), a core region of the emotion regulation network.

RESULTS

Consistent with our hypothesis that individuals with high ACEs have difficulty relying on social support, we observed a significant negative relationship between targets' cumulative ACEs and distress relief during the distressing condition. Neuroimaging revealed that higher ACEs scores were significantly linked to differential interbrain coupling patterns in the DLPFC: increased coupling during the distressing condition and decreased coupling during the neutral condition.

CONCLUSIONS

Among higher ACEs dyads, hyper interbrain coupling during distress may suggest heightened yet unsuccessful efforts to regulate distress, while hypo interbrain coupling in non-distressing situations may indicate poor connectedness in neutral social interactions. Therefore, abnormal interbrain coupling may underlie the difficulties high ACEs individuals face in benefiting from supportive interactions.

The mediating role of adult attachment styles between early traumas and suicidal behaviour

Our Hungarian cross-sectional study highlights the crucial mediating role that adult attachment styles play in the relationship between early traumas and suicidal behaviour, shaping how individuals process and respond to traumatic experiences. Early traumas, such as abuse or neglect, often disrupt the development of secure attachment, leading to insecure styles in adulthood-such as anxious or avoidant attachment. These insecure attachment styles influence emotional regulation, interpersonal relationships, and coping mechanisms, thereby exacerbating feelings of isolation and despair. For instance, anxious attachment can intensify fear of abandonment and hypersensitivity to rejection, increasing emotional instability and suicidal ideation. Conversely, avoidant attachment may lead to emotional suppression and reluctance to seek support, amplifying feelings of hopelessness. Psychopathological symptoms resulting from early trauma-such as depression and PTSD-are often filtered through these attachment patterns, shaping how distress is experienced and managed. In our research, we analysed the role of adult attachment styles and early traumas in suicidal behaviour. We also examined the mediating effect of attachment style in the relationship between early traumas and suicidal behaviour. A total of 357 subjects between the ages of 18 and 85 (mean = 37.02, SD = 12.86) were included in the analysis; 33.6% were male and 66.4% female. The sample consisted of 146 individuals with a history of suicide, 154 clinical participants without a history of suicide, and 57 from a non-clinical population. The adult attachment scale (AAS) and the childhood trauma questionnaire (CTQ) were used as assessment tools. To model the relationships between variables, logistic regression, generalized linear models, and mediation analyses were conducted. All models were adjusted for basic demographic variables. Our results showed that the severity of emotional abuse (adjusted OR 1.064, p = 0.004), emotional neglect (adjusted OR 1.064, p = 0.007), and overall traumatization measured by the CTQ (adjusted OR 1.021, p = 0.006) significantly predicted a higher risk of suicidal behaviour. In contrast, higher levels of secure attachment style predicted a lower risk of suicide attempt (adjusted OR -0.091, p = 0.004). Additionally, secure attachment style significantly mediated part of the total effect of early traumatization severity on suicidal behaviour (indirect effect = 0.0032, p < 0.05; Pm = 16.5%). We also examined the relationship between early traumas and attachment style and found multiple significant associations. For avoidant attachment, significant associations were observed with the total traumatization score (B = 0.086, p < 0.001) and specific adversities, including emotional abuse, emotional neglect, and physical neglect (B = 0.244-0.319, all p < 0.001). Anxious-ambivalent attachment was associated with the total CTQ score (B = 0.088, p < 0.001), as well as emotional abuse (B = 0.298, p < 0.001), emotional neglect (B = 0.254, p < 0.001), physical abuse (B = 0.248, p < 0.001), and physical neglect (B = 0.261, p = 0.010). A lower level of secure attachment was linked to the overall traumatization score (B = -0.039, p = 0.004), as well as emotional abuse, emotional neglect, and sexual abuse (B = -0.101 to -0.163, all p < 0.05). By mediating the relationship between trauma and suicidal behaviour, adult attachment styles can either perpetuate maladaptive coping strategies or hinder recovery. Understanding this mediating role is crucial for developing interventions that address attachment insecurities while promoting resilience and emotional healing. Therapeutic approaches aimed at fostering secure attachment patterns can help mitigate the effects of early trauma and reduce the risk of suicidal behaviour. These findings underscore the importance of incorporating attachment-focused strategies into trauma-informed care.

Childhood Homelessness as an Adverse Childhood Experience (ACE): Adult Mental Health Outcomes

Adverse childhood experiences (ACEs) are experiences of abuse, neglect, and other household problems occurring before age 18 and contribute to the development of both physical and mental health concerns. People experiencing homelessness report disproportionately higher rates of ACEs and negative mental health concerns; however, little research has been conducted regarding the relationship between ACEs and mental health outcomes specifically for homeless populations. A dearth of research also exists regarding how childhood experiences of homelessness interact with ACEs and mental health outcomes. The present study examined the mental health outcomes for people experiencing homelessness, as well as how childhood experiences of homelessness may fit into the ACEs model using archival data. People experiencing homelessness (n = 100) completed the ACEs questionnaire, a demographics questionnaire, and a health appraisal questionnaire. Results found ACEs significantly predicted negative mental health outcomes for people experiencing homelessness. Childhood experiences of homelessness were predictive of negative mental health outcomes; however, this relationship became negligible when acting as a covariate with ACEs. This result suggests that the ACEs framework adequately explains the effects of traumatic events for children experiencing homelessness and the subsequent negative mental health outcomes.

Psychometric Properties of the Adverse Childhood Experiences Abuse Short Form (ACE-ASF) for Ecuadorian Youth

Adverse childhood experiences, such as abuse, are a risk factor for mental health and poor socio-emotional development in adulthood. Assessing these experiences in specific populations allows for the identification of patterns and the implementation of preventive interventions.

OBJECTIVE

To evaluate the psychometric properties of the abbreviated version of the Adverse Childhood Experiences Abuse Form (ACE-ASF) in Ecuadorian youth, aiming to ensure the validity, reliability, and consistency of the instrument in accurately measuring abuse dimensions in this Ecuadorian population.

METHODOLOGY

An instrumental study was conducted on the psychometric properties of the eight-item ACE-ASF, applying it to a sample of 840 university students (52.1% females and 47.9% males). The evaluation focused on analyzing the factorial structure and internal consistency of the instrument in this sample.

RESULTS

The two-factor model showed a satisfactory fit across all levels of invariance (configural, metric, scalar, and strict), with acceptable fit indices (CFI, TLI, GFI, RMSEA, and SRMR). The internal consistency was adequate, as assessed using the McDonald's omega and Cronbach's alpha coefficients. Convergent and discriminant validity were confirmed using the AVE and HTMT indices, ensuring proper differentiation between the dimensions assessed.

CONCLUSION

The ACE-ASF proved to be a valid and reliable instrument for assessing abuse experiences in Ecuadorian youth. Its two-factor structure reflects distinct yet related dimensions, providing a useful tool for identifying adverse childhood experiences in this population.

Adverse and benevolent childhood experiences moderate the association between PTSD symptoms and suicidal ideation

Posttraumatic stress disorder (PTSD) symptoms are a robust risk factor for SI. Adverse childhood experiences (ACEs) can increase the risk for SI in the context of PTSD symptoms. Social support has been shown to buffer the impact of ACEs on SI. The current study aimed to examine the interaction between benevolent childhood experiences (BCEs), ACEs, and PTSD symptoms on SI. We administered a questionnaire to 837 undergraduate students (MAge = 19.1; 88.3% White; 76.3% women). The three-way interaction between ACEs, BCEs, and PTSD symptoms on SI was significant, F(9,721) = 49.89, p < .001, and accounted for 38.38% of the variance in SI. The results of our study suggest that BCEs would weaken the relationship between PTSD symptoms and SI, regardless of ACE-level. These findings may inform future suicide research, prevention, and intervention efforts.

The Association between Childhood Adversity and the Conserved Transcriptional Response to Adversity (CTRA) in Sexual Minority Men

Adverse childhood experiences (ACEs) increase risk for mental and physical health disorders in adulthood, particularly in individuals from sexual and ethnic minority groups. The effects of ACEs on health may be mediated by the immune system. The exact mechanisms by which an environmental exposure, such as childhood adversity, can affect the immune system are still unknown. The primary aim of this study was to determine whether early adversity is associated with significant changes in the expression of a predefined set of immune-related genes, known as the conserved transcriptional response to adversity (CTRA), in a diverse group (African American and Latino) of sexual minority men (SMM) (n = 259). Participants included HIV positive and negative males, with a median age of 31 years (range = 19-46 years), from the mSTUDY. Expression data from 53 CTRA genes were obtained at baseline and 12-month follow-up. Childhood adversity was measured with the 10-item ACEs questionnaire. Wilcoxon rank sum and chi-squared tests were used to assess differences in sociodemographic variables, HIV status, smoking, weekly alcohol use, and methamphetamine use between exposed (cumulative ACEs ≥ 1) and unexposed groups (cumulative ACEs = 0). As we had transcriptional data from two timepoints, linear mixed models were used to determine associations between ACEs (cumulative score, dichotomous measure (exposed/unexposed), childhood maltreatment, household dysfunction, abuse and neglect subscales) and CTRA gene expression. Exploratory subgroup analysis was conducted in younger (≤ median age) and older (> median age) participant groups. There were no statistically significant differences in sociodemographic variables and substance use between the exposed and unexposed groups. There were no significant associations between any of the ACEs variables and CTRA gene, suggesting that early adversity does not influence immune-related gene expression in a group of ethnically diverse SMM. Further studies are needed to assess the biological effects of ACEs in adulthood.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40653-024-00661-2.

Effectiveness of Adaptation of a Resilience-Building Intervention Among Individuals With Adverse Childhood Experience: Protocol for a Randomized Controlled Trial

BACKGROUND

The impact of adverse childhood experiences (ACEs) has been the focus of most studies for the past decade. There is an indication that developing resilience can help youth overcome these ACEs.

OBJECTIVE

This article presents a study protocol for a randomized controlled trial (RCT) to investigate the effects of a resilience-building intervention on psychological well-being, coping strategies, stress, quality of life, resilience, resource finding, and resilience among individuals affected with ACEs in Malaysia.

METHODS

The is a 2-armed, single-blind, RCT, whereby 50 participants (25 in each group) with ACEs will be randomly assigned to intervention and control groups. The former will be exposed to a resilience-building program (R2), which entails a multisystemic approach to resilience and recognizes the importance of rugged qualities and access to resources among individuals affected with ACEs. The intervention will be delivered via internet-based by a facilitator and broadly divided into 5 sessions, focusing on self-exploration and social support, coping techniques and coping skills, resource finding, spirituality, and resilience building. Meanwhile, the control group participants will not receive any form of intervention. Saliva samples will also be collected from both groups and assessed for salivary cortisol levels. Outcome measures will be assessed during baseline and postintervention using validated instruments. Another follow-up measurement will be conducted 4 weeks later.

RESULTS

The clinical trial has been registered with the Australia New Zealand Clinical Trials Registry. Ethical approval was obtained from the Research Ethics Board at the National University of Malaysia (UKM PPI/111/8/JEP-2021-894). A total of 28 participants have been recruited to the RCT Participant recruitment will be completed by January 2025. The final analysis will be conducted by March 2025.

CONCLUSIONS

This is among the first studies to provide evidence in the context of RCTs for resilience-building intervention that combines self-report and physiological measures (ie, saliva and heart blood pressure) among individuals with ACEs. The findings will assist relevant authorities in the health and policy sectors to develop effective strategies for addressing the negative impacts of ACEs on the vulnerable population in Malaysia.

TRIAL REGISTRATION

ACTRN12622000604707; https://www.anzctr.org.au/Trial/Result/DataSharingStatement.aspx?id=383614.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/56826.

Prevalence of Adverse Childhood Experiences in Child Population Samples: A Systematic Review and Meta-Analysis

Importance

Exposure to adverse childhood experiences (ACEs) before the age of 18 years is a major contributor to the global burden of disease and disability.

Objective

To meta-analyze data from samples with children 18 years or younger to estimate the average prevalence of ACEs, identify characteristics and contexts associated with higher or lower ACE exposure, and explore methodological factors that might influence these prevalence estimates.

Design, Setting, and Participants

Studies that were published between January 1, 1998 and February 19, 2024, were sourced from MEDLINE, PsycINFO, CINHAL, and Embase. Inclusion criteria required studies to report the prevalence of 0, 1, 2, 3, or 4 or more ACEs using an 8- or 10-item ACEs questionnaire (plus or minus 2 items), include population samples of children 18 years or younger, and be published in English. Data from 65 studies, representing 490 423 children from 18 countries, were extracted and synthesized using a multicategory prevalence meta-analysis. These data were analyzed from February 20, 2024, through May 17, 2024.

Main Outcomes and Measures

ACEs.

Results

The mean age of children across studies was 11.9 (SD, 4.3) years, the age range across samples was 0 to 18 years, and 50.5% were female. The estimated mean prevalences were 42.3% for 0 ACEs (95% CI, 25.3%-52.7%), 22.0% for 1 ACE (95% CI, 9.9%-32.7%), 12.7% for 2 ACEs (95% CI, 3.8%-22.3%), 8.1% for 3 ACEs (95% CI, 1.4%-16.8%), and 14.8% for 4 or more ACEs (95% CI, 5.1%-24.8%). The prevalence of 4 or more ACEs was higher among adolescents vs children (prevalence ratio, 1.16; 95% CI, 1.04-1.30), children in residential care (1.26; 95% CI, 1.10-1.43), with a history of juvenile offending (95% CI, 1.29; 1.24-1.34), and in Indigenous peoples (1.63; 95% CI, 1.28-2.08), as well as in studies where file review was the primary assessment method (1.29; 95% CI, 1.23-1.34). The prevalence of 0 ACEs was lower in questionnaire-based studies where children vs parents were informants (0.85; 95% CI, 0.80-0.90).

Conclusions

In this study, ACEs were prevalent among children with notable disparities across participant demographic characteristics and contexts. As principal antecedent threats to child and adolescent well-being that can affect later life prospects, ACEs represent a pressing global social issue. Effective early identification and prevention strategies, including targeted codesigned community interventions, can reduce the prevalence of ACEs and mitigate their severe effects, thereby minimizing the harmful health consequences of childhood adversity in future generations.

Adverse Childhood Experiences Moderate the Relationship Between Pain and Later Suicidality Severity Among Youth: A Longitudinal High-Risk Cohort Study

Pain in adolescence can lead to the development of serious mental health issues, including suicidality. This risk may be strengthened among youth exposed to more adverse childhood experiences (ACEs; abuse, neglect, household challenges). This longitudinal study examined the role of ACEs in the relationship between pain and later suicidality onset and severity among a cohort of adolescents at risk for developing mental health problems. Participants were 139 healthy youth (Mage = 13.74 years, standard deviation = 1.56, 64% female) between the ages of 11 to 17 years, recruited based on parental history of depression or anxiety. Youth completed validated measures of internalizing symptoms, ACEs, and pain characteristics at baseline and follow-up diagnostic interviews 9 and/or 18 months later to assess for onset and severity of suicidality. After controlling for demographics, baseline internalizing symptoms, and ACEs, worse pain interference and increased ACEs at baseline predicted increased suicidality severity at follow-up. Moderation analyses revealed that there was a significant interaction between ACEs and pain interference and pain intensity. Increased pain interference (b = 7.65, P < .0001) or intensity (b = 6.96, P = .0003) was only associated with increased suicidality severity at follow-up in youth with high levels of ACEs. This study demonstrates that ACEs strengthen the relationship between pain and later suicidality severity among youth at risk of developing mental health problems. Findings underscore the critical need to adopt a trauma-informed lens to pediatric pain prevention and treatment (eg, screening for ACEs) and for the pain to be on the child's mental health agenda. PERSPECTIVE: This article provides evidence that, while pain is a risk factor for future increased suicidality severity, it is a particularly strong risk factor in youth who experienced increased childhood adversity. These results may help identify youth at greatest risk for suicidality.

How adverse childhood experiences impact the professional quality of life of residential care workers: resilience as a mediator for burnout, secondary traumatic stress, and compassion satisfaction

Introduction

The well-being of trauma-affected children and youth in residential care settings is contingent upon the well-being of the workers who care for them, who are increasingly expected to provide care in a trauma-informed manner. The well-being of residential care workers (RCWs) may be impacted by their own histories of adversity, their capacity individually and collectively to navigate to resources that sustain their well-being (resilience), and current perceptions of their professional quality of life.

Objective

This study aimed to fill a research gap by canvassing the perspectives of RCWs to determine what and how they need to be supported in their work. We sought to better understand what personal (adverse childhood experiences, resilience) and professional (compassion satisfaction, burnout, secondary traumatic stress) experiences and capacities they bring into their work that might impact the quality of care they provide to children and youth.

Method

A sample of 226 residential care workers from four residential care organizations across three Canadian provinces completed a self-report questionnaire to provide a portrait of their history of adverse childhood experiences as measured by the ACE questionnaire, which included two additional questions reflecting the more nuanced and expanded understanding of potential adversity in childhood in the Canadian context; their resilience, as measured by the Adult Resilience Measure; and compassion satisfaction, burnout, and secondary traumatic stress, as measured by the Professional Quality of Life Measure. Mediation was conducted to examine whether and how resilience mediated the relationship between ACEs and professional quality of life indicators.

Results

(1) RCWs reported experiencing ACEs at rates much higher than general population and norm samples, especially regarding the experience of 4-5+ ACEs, known to be a threshold for increased severity in negative outcomes; (2) RCWs experienced levels of resilience and indicators of professional quality of life similar to those in other human services professions serving trauma-impacted individuals; and (3) RCW resilience significantly mediated the relationship between ACEs and compassion satisfaction, burnout, and secondary traumatic stress, and had a significant total effect for the relationship between ACEs and secondary traumatic stress. These results suggest the importance of enhancing RCW resilience in multiple ways, mainly in their professional contexts. Recommendations for resilience enhancement and suggestions for future research are provided.

Patterns of adverse childhood experiences and associations with lower mental well-being among university students

BACKGROUND

University students report high levels of adverse childhood experiences (ACEs), which can lead to severe mental health problems. Understanding how ACEs impact well-being in this population is essential, yet research to date is limited.

OBJECTIVE

To explore ACE patterns and their association with lower well-being in university students.

PARTICIPANTS AND SETTING

1023 Spanish students (71.6 % female) aged between 18 and 64 years old (M = 20.10, SD = 3.93) completed a self-report questionnaire.

METHODS

This study used a cross-sectional design. The ACE International Questionnaire (ACE-IQ) and the Short Warwick-Edinburgh Mental Well-being Scale were used to assess, respectively, childhood adversities and mental well-being. Latent Class Analysis and regression modeling were conducted to analyze the link between ACEs and lower mental well-being, considering the covariates of age, country of origin, sexual orientation, and mental illness.

RESULTS

Four ACE classes were identified: Low ACEs (49.5 %), Dysfunctional Household (12.3 %), Household and Peer Abuse (31.0 %), and High ACEs (7.2 %). The regression analysis (F(3, 1007) = 19.2, p < .001, R2adj = 0.054) successfully predicted well-being scores based on ACE classes. When compared with the Low ACE class, all other classes exhibited lower levels of well-being. Age, sexual orientation, and mental illness were also related to lower well-being, with mental illness having the strongest negative effect (β = -0.635, t(1015) = -6.49, p < .001).

CONCLUSIONS

These findings underscore the relationship between childhood adversity and mental health, offering insights for future prevention efforts and enriching our understanding of ACEs and their impact on well-being.

Exploring stress response's role in executive function impairments among adults with early adverse childhood experiences

Adverse childhood experiences (ACEs) are recognised as precursors to numerous physical and mental health challenges. However, research on their impact on inhibitory control and working memory, particularly among healthy young adults, remains limited. The role played by the stress response as a moderator in these effects is likewise underexplored. Our study addresses this gap by examining cognitive impairments in non-clinical adults with early childhood trauma, specifically trauma before the age of 13 years, and by assessing the influence of the stress response on these effects. A total of 15 participants with early ACEs were compared with a control group (n = 18) using the Corsi Block Tapping Test (CBTT) and Stroop Word Colour Test (SCWT). Results showed that participants with early ACEs exhibited lower scores on the SCWT but not the CBTT. The stress response emerged as a potential factor in the relationship between early ACEs and cognitive performance. The implications of these findings are then discussed in relation to the existing literature.

Validity and reliability of the 10-Item Adverse Childhood Experiences Questionnaire (ACE-10) among adolescents in the child welfare system

Introduction

Multiple evidence suggests that the vast majority of children in the Child Welfare System (CWS) are victims of early, chronic, and multiple adverse childhood experiences. However, the 10-item version of the Adverse Childhood Experiences Questionnaire (ACE-10) has never been tested in such a particularly vulnerable population as adolescents living in the CWS. We aimed to assess the psychometric properties of the ACE-10 in a community sample of 240 Hungarian adolescents placed in family style group care (FGC) setting.

Methods

Demographic data, the 10-item version of the Adverse Childhood Experiences Questionnaire (ACE-10), the Strengths and Difficulties Questionnaire (SDQ), and the HBSC Bullying Measure were used.

Results

Our results showed acceptable internal consistency (α = 0.701) and item-total correlations (rpb = 0.25-0.65, p < 0.001). However, our results also reflect that item 6 ("Parental separation/divorce") is weakly correlated with both the cumulative ACE score and the rest of the questionnaire items. When item 6 is removed, the 9-item version of the ACE produces more favorable consistency results (α = 0.729). Strong and significant associations of the cumulative ACE score with emotional and behavioral symptoms and bully victimization confirm the concurrent criterion validity of both versions of the instrument.

Discussion

Our findings suggest that ACE-9 and ACE-10 are viable screening tools for adverse childhood experiences in the CWS contributing to the advancement of trauma-informed care. We recommend considering the use of either the 9-item or the 10- item version in the light of the characteristics of the surveyed population. The implications and limitations are discussed.