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.     

Nest sanitation as an effective defence against brood parasitism

Animal Cognition - Egg rejection is a crucial defence strategy against brood parasitism that requires the host to correctly recognise the foreign egg. Rejection behaviour has, thus, evolved in many...     

Remaining or becoming secure: Parental sensitive support predicts attachment continuity from infancy to adolescence in a longitudinal adoption study

In a longitudinal study with 125 early adopted adolescents, we examined continuity of attachment from infancy to adolescence and the role of parental sensitive support in explaining continuity or discontinuity of attachment. Assessments of maternal sensitive support and infant attachment (Strange Situation Procedure) were completed when infants were 12 months old. When the children were 14 years old, we observed mothers' sensitive support during a conflict discussion. The adolescents' attachment representations were assessed with the Adult Attachment Interview. Mothers of secure adolescents showed significantly more sensitive support during conflicts than did mothers of insecure adolescents. Overall, no continuity of attachment from infancy to adolescence was found. However, maternal sensitive support in early childhood and adolescence predicted continuity of secure attachment from 1 to 14 years, whereas less maternal sensitive support in early childhood but more maternal sensitive support in adolescence predicted children's change from insecurity in infancy to security in adolescence. We conclude that both early and later parental sensitive support are important for continuity of attachment across the first 14 years of life. (PsycINFO Database Record (c) 2012 APA, all rights reserved).