Mariëlle Linting

Nonlinear Principal Components Analysis: Introduction and Application.

The authors provide a didactic treatment of nonlinear (categorical) principal components analysis (PCA). This method is the nonlinear equivalent of standard PCA and reduces the observed variables to a number of uncorrelated principal components. The most important advantages of nonlinear over linear PCA are that it incorporates nominal and ordinal variables and that it can handle and discover nonlinear relationships between variables. Also, nonlinear PCA can deal with variables at their appropriate measurement level; for example, it can treat Likert-type scales ordinally instead of numerically. Every observed value of a variable can be referred to as a category. While performing PCA, nonlinear PCA converts every category to a numeric value, in accordance with the variables analysis level, using optimal quantification. The authors discuss how optimal quantification is carried out, what analysis levels are, which decisions have to be made when applying nonlinear PCA, and how the results can be interpreted. The strengths and limitations of the method are discussed. An example applying nonlinear PCA to empirical data using the program CATPCA (J. J. Meulman, W. J. Heiser, & SPSS, 2004) is provided.

Nonlinear Principal Components Analysis With CATPCA: A Tutorial

This article is set up as a tutorial for nonlinear principal components analysis (NLPCA), systematically guiding the reader through the process of analyzing actual data on personality assessment by the Rorschach Inkblot Test. NLPCA is a more flexible alternative to linear PCA that can handle the analysis of possibly nonlinearly related variables with different types of measurement level. The method is particularly suited to analyze nominal (qualitative) and ordinal (e.g., Likert-type) data, possibly combined with numeric data. The program CATPCA from the Categories module in SPSS is used in the analyses, but the method description can easily be generalized to other software packages.

Children’s hair cortisol as a biomarker of stress at school entry

Abstract Quantification of cortisol in scalp hair seems a promising measurement for long-term cortisol levels, and thereby a biomarker for stress. We examined hair cortisol concentrations (HCC) in children when first entering elementary school. Participants were 42 children (45% boys) with a mean age of 4.2 years (SD = 0.42 months). Hair samples (≥5 cm) were collected 2 months after school entry. Hair analysis was conducted using two 2-cm long segments, reflecting the first 2 months of school attendance (the scalp-near segment) and 2 months prior to school entry. HCC were higher after school entry than before, especially for fearful children. Alterations in HCC were not moderated by experience in group daycare before school entry. Thus, HCC suggest that starting elementary school is accompanied by increased stress hormone levels in young (in particular fearful) children.

Electrodermal reactivity during the Trier Social Stress Test for children: Interaction between the serotonin transporter polymorphism and children's attachment representation

This study explores the relation between variations in the serotonin transporter gene (5-HTTLPR; long vs. short allele), the childs attachment representation (assessed with the Attachment Story Completion Task, reflecting the security of the parent-child relationship), and electrodermal reactivity during a public speaking task, the Trier Social Stress Test for Children (TSST-C) in a sample of 92 7-year-old. Electrodermal reactivity during the TSST-C was not directly associated with variations in 5-HTT. However, there was a significant gene-environment interaction effect of 5-HTT and attachment security on electrodermal reactivity. Results are interpreted in terms of cumulative protection: Children with a secure attachment representation as well as long 5-HTT alleles appeared to be less stressed during the TSST-C.

Stability of Nonlinear Principal Components Analysis: An Empirical Study Using the Balanced Bootstrap

Principal components analysis (PCA) is used to explore the structure of data sets containing linearly related numeric variables. Alternatively, nonlinear PCA can handle possibly nonlinearly related numeric as well as nonnumeric variables. For linear PCA, the stability of its solution can be established under the assumption of multivariate normality. For nonlinear PCA, however, standard options for establishing stability are not provided. The authors use the nonparametric bootstrap procedure to assess the stability of nonlinear PCA results, applied to empirical data. They use confidence intervals for the variable transformations and confidence ellipses for the eigenvalues, the component loadings, and the person scores. They discuss the balanced version of the bootstrap, bias estimation, and Procrustes rotation. To provide a benchmark, the same bootstrap procedure is applied to linear PCA on the same data. On the basis of the results, the authors advise using at least 1,000 bootstrap samples, using Procrustes rotation on the bootstrap results, examining the bootstrap distributions along with the confidence regions, and merging categories with small marginal frequencies to reduce the variance of the bootstrap results.

Enhancing home-based child care quality through video-feedback intervention: a randomized controlled trial.

In the present randomized controlled trial, the effectiveness of video-feedback intervention to promote positive parenting-child care (VIPP-CC) was tested in home-based child care. Forty-eight caregivers were randomly assigned either to the intervention group or to the control group. Global child care quality improved in the intervention group but not in the control group. The program did not change observed caregiver sensitivity. After the intervention however, caregivers in the intervention group reported a more positive attitude toward sensitive caregiving than caregivers in the control group. The study shows that the family-based intervention can be applied with some minor modifications in a professional group setting as well. The brief VIPP-CC program is an important tool for enhancing quality of home-based child care.

The relation of flexible child care to quality of center day care and children's socio-emotional functioning: A survey and observational study

In two studies in daycare centers, we investigated a newly developed index for flexible child care describing parents’ use of evening care and flexible attendance scheduling for their child. We examined the relation between this index together with stability in care, mother’s stress and the child’s temperament on the one hand, and quality of caregivers’ behavior and a child’s socio-emotional functioning in day care on the other. In Study I, the mothers and caregivers of 186 children (aged 6–30 months) participated in a survey. In Study II, approximately 18 months later, 52 children from Study I were observed in their daycare setting. Children showed more well-being in day care when they had few parallel care arrangements, and when there was more daily stability in staffing and grouping patterns. Unexpectedly, caregivers in groups with more stability in staffing and grouping patterns, showed less positive caregiving behavior. When staff turnover rate was higher, positive caregiving behavior was lower. Finally, children in more flexible child care showed more non-compliance.

The role of oxytocin in familiarization-habituation responses to social novelty.

Stress or arousal responses to novel social contexts ease off when individuals get familiar with the social context. In the present study we investigated whether oxytocin is involved in this process of familiarization-habituation as oxytocin is known to increase trust and decrease anxiety. Fifty-nine healthy female subjects took part in the same experimental procedure in two sessions separated by 4 weeks. In the first (novelty) session state trust scores were significantly positively correlated with salivary oxytocin levels while in the second (familiarity) session state trust scores were significantly negatively correlated with salivary oxytocin levels. In a path model oxytocin was associated with increased trust in the novelty session and trust was associated with decreased oxytocin levels in the familiarity session. The results are consistent with the idea that oxytocin decreases stress-to-novelty responses by promoting familiarization to novel social contexts.

Maternal Sensitivity and Internalizing Problems: Evidence from Two Longitudinal Studies in Early Childhood

The goal of this study is to clarify the relation between maternal sensitivity and internalizing problems during the preschool period. For this purpose, a longitudinal, bidirectional model was tested in two large prospective, population-based cohorts, the Generation R Study and the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (NICHD SECCYD), including over 1,800 mother–child dyads in total. Maternal sensitivity was repeatedly observed in mother–child interaction tasks and information on child internalizing problems was obtained from maternal reports. Modest but consistent associations between maternal sensitivity and internalizing problems were found in both cohorts, confirming the importance of sensitive parenting for positive development in the preschool years. Pathways from maternal sensitivity to child internalizing problems were consistently observed but child-to-mother pathways were only found in the NICHD SECCYD sample.

Differential susceptibility in a developmental perspective: DRD4 and maternal sensitivity predicting externalizing behavior

This study is the first to investigate the longitudinal effects of gene-environment interplay between DRD4 genotype and maternal sensitivity on child externalizing behavior. Multiple measures of maternal sensitivity (14, 36, and 48 months) and externalizing behavior (18 months, 36 months, and 5 years) were assessed in a large cohort study (N = 548). Early maternal insensitivity (14 months) was associated with early externalizing behavior (18 months) in a for better and for worse manner, but only in children with at least one DRD4 7-repeat, consistent with a differential susceptibility model. Later insensitivity (48 months) predicted externalizing behavior at age 5 independent of DRD4 genotype. A structural equation model including all measures across time supported the differential susceptibility model: The overall effect of early maternal sensitivity on later externalizing behavior was significant only for children with a DRD4 7-repeat allele. The results highlight the importance of studying gene-environment interactions across development.