Computational aspects of the greatest lower bound to the reliability and constrained minimum trace factor analysis

In the last decade several algorithms for computing the greatest lower bound to reliability or the constrained minimum-trace communality solution in factor analysis have been developed. In this paper convergence properties of these methods are examined. Instead of using Lagrange multipliers a new theorem is applied that gives a sufficient condition for a symmetric matrix to be Gramian. Whereas computational pitfalls for two methods suggested by Woodhouse and Jackson can be constructed it is shown that a slightly modified version of one method suggested by Bentler and Woodward can safely be applied to any set of data. A uniqueness proof for the solution desired is offered.The authors are obliged to Charles Lewis and Dirk Knol for helpful comments, and to Frank Brokken and Henk Camstra for developing computer programs.     

The Concept of Abnormality in Medical Genetics

This paper explores usage of the concept ofabnormality in medical genetics and proposesdirectives for more careful usage of this concept.The conceptual difficulties are first explored, thena model is developed to assess actual usage, followedby analysis of a sample of genetic textbooks andgenetics literature. It appears that fact andvaluation are often intermingled, that referencestandards used to define 'genetic abnormalities' areoften not clear and that the concept of abnormality isoften used independent of the degree of certainty withwhich the altered genetype develops into a (seriously)harmful phenotype. On the basis of these findings itis argued that more restraint and more careful use ofthe concept of genetic abnormality of medical geneticsis appropriate as well as more agreement on the use ofreference standards.     

On the equivalence of two oblique congruence rotation methods,and orthogonal approximations

Tucker's method of oblique congruence rotation is shown to be equivalent to a procedure by Meredith. This implies that Monte Carlo studies on congruence by Nesselroade, Baltes and Labouvie and by Korth and Tucker are highly comparable. The problem of rotating two matrices orthogonally to maximal congruence has not yet been solved. An approximate solution to this problem can be derived from Tucker's method. Even better results can be obtained from a Procrustes rotation followed by rotation to simple structure.     

A general solution for a class of weakly constrained linear regression problems

This paper contains a globally optimal solution for a class of functions composed of a linear regression function and a penalty function for the sum of squared regression weights. Global optimality is obtained from inequalities rather than from partial derivatives of a Lagrangian function. Applications arise in multidimensional scaling of symmetric or rectangular matrices of squared distances, in Procrustes analysis, and in ridge regression analysis. The similarity of existing solutions for these applications is explained by considering them as special cases of the general class of functions addressed.The author is obliged to Henk Kiers and Willem Heiser for helpful comments.     

Are memories for sexually traumatic events "special"? A within-subjects investigation of trauma and memory in a clinical sample

According to a long-standing clinical tradition, sexually traumatic experiences are processed and recalled differently from other experiences, often leading to memory impairment. In this study, we compared the characteristics of traumatic memories for sexual violence and two other types of emotional experiences. N=44 women recruited from a local sexual trauma agency were asked to recall and describe three autobiographical events: sexual abuse/assault, a non-sexual trauma, and a positive emotional event. The characteristics of the three memory types were compared on both subjective and objective measures. Further, the potential influences of level of traumatic impact and dissociation were assessed. Results indicated that memories for sexual trauma were not impaired or fragmented relative to other memories. Instead, memories for sexual trauma were associated with a remarkably high level of vividness, detail, and sensory components. Further, high levels of traumatic impact were not associated with memory impairment. Implications for the ongoing traumatic memory debate are discussed.     

Physiological correlates of intellectual function in children with sickle cell disease: hypoxaemia, hyperaemia and brain infarction

Lowered intelligence relative to controls is evident by mid-childhood in children with sickle cell disease. There is consensus that brain infarct contributes to this deficit, but the subtle lowering of IQ in children with normal MRI scans might be accounted for by chronic systemic complications leading to insufficient oxygen delivery to the brain. We investigated the relationship between daytime oxyhaemoglobin saturation (SpO2), cerebral blood flow velocity (CBFV) and intellectual function (IQ) using path-analysis in 30 adolescents with sickle cell disease (mean age 17.4 years, SD 4.2). Initial analyses revealed that the association between SpO2 and Full Scale IQ (FSIQ) was fully mediated by increased CBFV, whereby SpO2 was negatively correlated with CBFV and CBFV was negatively correlated with FSIQ, i.e. decreases in oxygen saturation are associated with increases in velocity, and increased velocity is associated with lowered IQ scores. The mediated relationship suggests that lowered IQ may be a function of abnormal oxygen delivery to the brain. Further analyses showed that the association between CBFV and IQ was significant for verbal but not for performance IQ. The pathophysiology characteristic of SCD can interfere with brain function and constrain intellectual development, even in the absence of an infarct. This supports the hypothesis that lowered intellectual function is partly explained by chronic hypoxia, and has wider implications for our understanding of SCD pathophysiology.     

Cybersex: regulating sexually explicit expression on the Internet

While the First Amendment restricts the power of the government to control access by adults to sexually explicit expression that is not obscene, the government may restrict access by children, provided that those restrictions do not limit adults to reading only "what is fit for children." Controlling access by children presents special problems in the context of broadcasting, because broadcast programming is accessible to children too young to read and because of the impossibility of segregating adults and children in the audience. The Supreme Court therefore permits the government to require "channeling" of sexually explicit programming to times when fewer unsupervised children are in the audience, to facilitate parental control over children's access to sexually explicit material. Although Internet content includes less than one percent of sexually explicit expression, that material has been the subject of intensive media and government attention. Much of that attention ignores (1) the high level of constitutional protection applicable to non-obscene, sexually explicit expression; (2) features of the Internet which facilitate controlling access by children to sexually explicit expression far more effectively than in broadcasting or print media; and (3) the First Amendment values served by permitting expression of all forms on the Internet.     

Testing models of the structure and development of future time perspective: maintaining a focus on opportunities in middle age

A core construct in socioemotional selectivity theory is future time perspective (FTP), conceptualized as a unidimensional and bipolar construct ranging from expansive to limited. Change in FTP across adulthood has been treated as linear, with older adults showing more limited FTP. Studies 1 and 2 showed that a 2-factor model fit better, with focus on opportunities and focus on limitations as distinct dimensions. These dimensions changed differentially with age. In cross-sectional Study 3, focus on opportunities was higher in young adulthood than in early middle age but did not drop further in late middle age. Focus on limitations was the same in young adulthood and early middle age but was higher in late middle age. In longitudinal Study 4, focus on limitations increased from early to late middle age, and focus on opportunities was again maintained, rather than showing the decrease one would assume from a 1-factor model of FTP.     

A generalization of Takane's algorithm for dedicom

An algorithm is described for fitting the DEDICOM model for the analysis of asymmetric data matrices. This algorithm generalizes an algorithm suggested by Takane in that it uses a damping parameter in the iterative process. Takane's algorithm does not always converge monotonically. Based on the generalized algorithm, a modification of Takane's algorithm is suggested such that this modified algorithm converges monotonically. It is suggested to choose as starting configurations for the algorithm those configurations that yield closed-form solutions in some special cases. Finally, a sufficient condition is described for monotonic convergence of Takane's original algorithm.Financial Support by the Netherlands organization for scientific research (NWO) is gratefully acknowledged. The authors are obliged to Richard Harshman.