Key Publications

• Bar-Haim, Y., Lamy, D., Pergamin, L., Bakermans-Kranenburg, M.J., & van IJzendoorn, M.H. (2007). Threat-related attentional bias in anxious and non-anxious individuals: A meta-analytic study. Psychological Bulletin, 133, 1-24.
  Abstract
  This meta-analysis of 172 studies (N=2,263 anxious, N=1,768 nonanxious) examined the boundary conditions of trheat-related attentional biases in anxietey. Overall, the results show that the bias is reliably demonstrated with different experimantal paradigms and under a variety of experimental conditions, but that it is only an effect size of d=0.45. Although processes requiring conscious perception of threat contribute to the bias, a significant comparable magnitude across different types of anxious populations (individuals with different clinical disorders, high-anxious nonclinical individuals, anxious children and adults) and is not observed in nonanxious individuals. Empirical and clinical implications as well as future directions for research are discussed.
  
• Madigan, S., Bakermans-Kranenburg, M.J., Van IJzendoorn, M.H., Moran, G., Pederson, D.R., & Benoit, D. (2006). Unresolved states of mind, anomalous parental behavior, and disorganized attachment: A review and meta-analysis of a transmission gap. Attachment and Human Development, 8, 89-111.
  Abstract
  The current meta-analysis examines the links between unresolved representations of attachment, anomalous parental behavior, and disorganized attachment relationships in 12 studies including 851 families. We found moderate effect sizes for the associations between unresolved states of mind and anomalous behavior (r=.26), unresolved states of mind and infant disorganized attachment relationships (r=.21), and anomalous behavior and disorganized attachment relationships (r=.34). Sample characteristics, observational context, and observational measure were not associated with differences in effect sizes. Only a small part of the association between unresolved states of mind and disorganized attachment relationships was explained by the mediation of anomalous parental behavior (.26*.34=.09). Other factors yet to be uncovered must mediate the influence of unresolved states of mind on infant disorganized attachment; thus, further exploration of infant, parental, ecological, and genetic factors are warrented.
  

• Van IJzendoorn, M. H., Juffer, F. & Klein Poelhuis, C.W. (2005). IQ and school achievement of adopted children: A meta-analytic comparison with non-adopted children . Psychological Bulletin, 131, 301-316.
  Abstract
  This meta-analysis of 62 studies (N=17,767 adopted children) examined whether the cognitive development of adopted children differed from that of (a) children who remained in institutional care of in the birth family and (b) their current (environmental) nonadopted siblings or peers. Adopted children scored higher in IQ tests than their nonadopted siblings or peers who stayed behind, and their school performance was better. Adopted children did not differ from their nonadopted environmental peers or siblings in IQ, but their school performance and language abilities lagged behind, and more adopted children developed learning problems. Taken together, the meta-analyses document the positive impact of adoption on the children's cognitive development and thei remarkably normal cognitive competence but delayed school performance. 
  
• Juffer, F., & Van IJzendoorn, M.H. (2005). Behavior problems and mental health referrals of international adoptees: A meta-analytic approach. JAMA, Journal of the American Medical Association, 293 (20), 2501-2515.
  Abstract
  Context: International adoption involves more than 40 000 children a year moving among more than 100 countries. Before adoption, international adoptees often experience insufficient medical care, malnutrition, maternal separation, and neglect and abuse in orphanages.
  Objective: To estimate the effects of international adoption on hebahioral problems and mental health referrals.
  Data Sources: We searched MEDLINE, PsychLit, and ERIC from 1950 to January 2005 using the terms adopt* combined with (behavior) problem, disorder, (mal)adjustment, (behavioral) development, clinical or psychiatric (referral), or mental health; conducted a manual search of the references of articles, books, book chapters, and reports; and consulted experts for relevant studies. The search was not limited to English-language publications.
  Study Selection: Studies that provided sufficient data to compute differences between adoptees (in all age ranges) and nonadopted controls were selected, resulting in 34 articles on mental health referrals and 64 articles on behavior problems.
  Data Extraction: Data on international adoption, preadoption adversity, and other moderators were extracted from each study and inserted in the program Comprehensive Meta-analysis (CMA). Effect sizes (d) for the overall differences between adoptees and controls regarding internalizing, externalizing, total behavior problems, and use of mental health services were computed. Homogeneity across studies was tested with the Q statistic.
  Data Synthesis: Among 25 281 cases and 80 260 controls, adoptees (both within and between countries) presented more behavior problems, but effect sizes were small (d, 0.16-0.24). Adoptees (5092 cases) were overrepresented in mental health services and this effect size was large (d, 0.72). Among 15 790 cases and 30 450 controls, international adoptees showed more behavior problems than nonadopted controls, but effect sizes were small (d, 0.07-0.11). International adoptees showed fewer total, externalizing and internalizing behavior problems than domestic adoptees. Also, international adoptees were less often referred to mental health services (d, 0.37) than domestic adoptees (d, 0.81). International adoptees with preadoption adversity showed more total problems and externalizing problems than international adoptees without evidence of extreme deprivation.
  Conclusions: Most international adoptees are well-adjusted although they are referred to mental health services more often than nonadopted controls. However, international adoptees present fewer behavior problems and are less often referred to mental health services than domestic adoptees.
  
• Vermeer, H.J., & Van IJzendoorn, M.H. (2006). Children’s elevated cortisol levels at daycare: A review and meta-analysis. Early Childhood Research Quarterly, 21, 390-401.
  Abstract
  We reviewed nine studies in which children's cortisol levels at center daycare were assessed. Our first hypothesis, concerning intraindividual differences in cortisol levels across home and daycare settings, was also tested in a meta-analysis. Our main finding was that at daycare children display higher cortisol levels compared to the home setting. Diurnal patterns revealed signigicant increases from morning to afternoon, but at daycare only. the combined effect size of seven pertinent studies (n=303) was r=.18 (Cl.06-0.29, p=.003). We examined all papers on possible associations between cortisol levels and quality care, and the influences of age, gender, and children's temperament. Age appeared to be the most significant moderator of this relation. It was shown that the effect of daycare attendance on cortisol excetion was especially notable in children younger than 36 months. We speculate that children in center daycare show elevated cortisol levels because of their stressful interactions in a group setting.
  
• Bakermans-Kranenburg, M.J., Van IJzendoorn, M.H., & Bradley, R.H. (2005). Those who have, receive: The Matthew effect in early childhood intervention in the home environment. Review of Educational Research, 75, 1-26.
  Abstract
  Are preventive early childhood interventions effective in improving home environments, as assessed with the HOME inventory (Caldwell & Bradley, 1984)? The authors traced 48 published articles, presenting 56 intervention effects (N=7,350). the combined effect size on the HOME total score was d= 0.20 (p<.001). Randomized intervention studies were effective, but the combined effect size was limited (d=0.13). Nonrandomized studies showed inflated effects (d=0.58). Interventions with middle-class, non-adolescent parents showed higher effect sizes than interventions with low-SES or adolescent samples. Effective interventions used a moderate number of sessions in a limited period and were home-based. Learning Materials, Involvement, and Responsitivity showed significant intervention effects. Families in better living conditions profited from parent education (the Matthew effect).
  
• Bakermans-Kranenburg, M.J., Van IJzendoorn, M.H., & Juffer, F. (2005). Disorganized infant attachment and preventive interventions: A review and meta-Analysis. Infant Mental Health Journal, 26, 191-216.
  Abstract
  Infant disorganized attachment is a major risk factor for problematic stress management and later problem behavior. Can the emergence of attachment disorganization be prevented? The current narrative review and quantitative meta-analysis involves 15 preventive interventions (N=842) that included infant disorganized attachment as an outcome measure. The effectiveness of the interventions ranged from negative to positive, with an overall effect size of d=0.05 (ns). Effective interventions started after 6 months of the infant's age (d=0.23). Interventions that focused on sensitivity only were significantly more effective in reducing attachment disorganization (d=0.24) than interventions that (also) focused on supprot and parent's mental represantations (d=-0.04). Most sample characteristics were not associated with differences in effect sizes, but studies  with children at risk were more successful (d=0.29) than studies with at-risk parents (d=-0.10), and studies on samples wiht higher percentages of disorganized attachment in the control group were more effective (d=0.31) than studies with lower percentages of disorganized children in the control group (d=-0.18). The meta-analysis shows that disorganized attachments may change as a side effect of sensitivity-focused interventions, but it also illustrates the need for interventions specifically focusing on the prevention of disorganization.
  
• Van IJzendoorn, M.H., Vereijken, C.M.J.L., Bakermans-Kranenburg, M.J., & Riksen-Walraven, J.M.A. (2004). Is the Attachment Q-Sort a valid measure of attachment security in young children? Child Development, 75, 1188-1213.
  Abstract
  The reliability and validity of the Attachment Q Sort (AQS; Waters & Deane, 1985) was tested in a series of meta-analyses on 139 studies with 13,835 children. The observer AQS security score showed convergent validity with Strange Situation procedure (SSP) security (r=.31) and excellent predictive validity with sensitivity measures (r=.39). Its association with temperament was weaker (r=.16), which supports the discriminant validity of the observer AQS. Studies on the stability of the observer AQS are still relatively scarce but they have yielded promising results (mean r=.28; k=4, n=162). It is concluded that the observer AQS, but not the self-reported AQS, is a valid measure of attachment.
  
• Rutgers, A.H., Bakermans-Kranenburg, M.J., Van IJzendoorn, M.H., & Van Berckelaer-Onnes, I.A. (2004). Autism and attachment:  A meta-analytic review. Journal of Child Psychology and Psychiatry, 45, 1123-1135.
  Abstract
  Method: Sixteen studies on attachment in children with autism were reviewed, and ten studies with data on observed attachment security (N=287) were included in a quantitative meta-analysis. Results: Despite the impairments of children with autism in reciprocal social interaction, the majority of the studies found evidence for attachment behaviours in these children. In four samples using the Strange Situation  procedure the average percentage of secure attachments amounted to 53% (n=72). Meta-analytic results showed that children with autism were significantly less securely attached to their parents than comparison children, and the combined effect size for this difference was moderate (r=.24). Children with autism displayed less attachment security than comparisons without autism, but this difference disappeared in samples with children with higher mental development, and in samples in which autism was mixed with less severe symptoms of autistic spectrum disorders. Conclusions: It is concluded that attachment security is compatible with autism, and can be assessed with Strange Situation type of procedures. The co-morbidity of autism and mental retardation appears to be associated with attachment insecurity.
  
• Bimmel, N., Juffer, F., Van IJzendoorn, M.H., & Bakermans-Kranenburg, M.J. (2003). Problem behavior of internationally adopted adolescents: A review and meta-analysis. Harvard Review of Psychiatry, 1, 64-77.
  Abstract
  In this paper we examine the prevalence of problem behaviors in samples of adolescents who were adopted from a foreign country as infants or young children. We reviewed ten studies and performed a meta-analysis, comparing 2317 internationally adopted adolescents with 14,345 nonadopted adolescents. Results indicate that internationally adopted adolescents exhibit more behavior problems than do nonadopted adolescents (d=0.08; p=0.02), with the difference seen in externalizing (d=0.11; p=0.00), but not in internalizing (d=0.05; p=0.12), behavior problems. Significantly more total behavior problems were seen in adopted than in nonadopted girls (d=0.10; p=0.03), but not in adopted boys compared to nonadopted ones (d=0.07; p=0.22). All differences, however, were small. The differences between adopted and nonadopted adolescents were somewhat larger when we considered behavior problems in the clinical range. The majority of the adopted adolescents are well adjusted and do not display significantly mor problem behaviors than do their nonadopted peers.
  
• Van IJzendoorn, M.H., Bakermans-Kranenburg, M.J., & Sagi, A. (2003). Are children of Holocaust survivors less well-adapted? No meta-analytic evidence for secondary traumatization. Journal of Traumatic Stress, 16, 459-469.
  Abstract
  H. Keilson (1979) coined the term "sequential traumatization" for the accumulation of traumatic stresses confronting the Holocaust survivors before, during, and after the war. A central question is whether survivors were able to raise their children without transmitting the traumas of their past. Through a series of meta-analyses on 32 samples involving 4,418 participants, we tested the hypothesis of secondary traumatization in Holocaust survivor families. In the set of adequately designed nonclinical studies, no evidence for the influence of the parent's traumatic Holocaust experiences on their children was found. Secondary traumatization emerged only in studies on clinical participants, whe were stressed for other reasons. A stress-diathesis model is used to interpret the absence of secondary traumatization in nonclinical offspring of Holocaust survivors.
  
• Bakermans-Kranenburg, M.J., Van IJzendoorn, M.H., & Juffer, F. (2003). Less is more: Meta-analyses of sensitivity and attachment interventions in early childhood. Psychological Bulletin, 129, 195-215.
  Abstract
  Is early preventive intervention effective in enhancing parental sensitivity and infant attachment security, and if so, what type of intervention is most successful? Seventy studies were traced, producing 88 intervention effects on sensitivity (n=7,636) and/or attachment (n=1,503). Randomized interventions appeared rather effective in changing insensitive parenting (d=0.33) and infant attachment insecurity (d=0.20). The most effective interventions used a moderate number of sessions and a clear-cut behavioral focus in families with, as well as without, multiple problems. Interventions that were more effective in enhancing parental sensitivity were also more effective in enhancing attachment security, which supports the notion of a causal role of sensitivity in shaping attachment.