The integration of continuous and discrete latent variable models: potential problems and promising opportunities

Structural equation mixture modeling (SEMM) integrates continuous and discrete latent variable models. Drawing on prior research on the relationships between continuous and discrete latent variable models, the authors identify 3 conditions that may lead to the estimation of spurious latent classes in SEMM: misspecification of the structural model, nonnormal continuous measures, and nonlinear relationships among observed and/or latent variables. When the objective of a SEMM analysis is the identification of latent classes, these conditions should be considered as alternative hypotheses and results should be interpreted cautiously. However, armed with greater knowledge about the estimation of SEMMs in practice, researchers can exploit the flexibility of the model to gain a fuller understanding of the phenomenon under study.     

Quality of life of adolescent males with attention-deficit hyperactivity disorder

Most psychosocial research on attention-deficit/hyperactivity disorder (ADHD) has focused on deficits in school, family, or behavioral functioning without incorporating perceived quality of life (QoL) or the adolescents' perspective. The Youth Quality of Life Instrument--Research Version (YQOL-R), was used to assess self-perceived QoL in a community sample of adolescents aged 11-18 years. Fifty-five adolescent males with a clinical diagnosis of ADHD were compared to a group of 107 adolescents with no chronic conditions (NCC) and a group of 52 adolescents with mobility impairments (MI). The adolescents with ADHD reported significantly lower perceived QoL scores, particularly in the Self and Relationship domains, than the NCC group. Their scores were similar to those from the group with MI, a group previously shown to have a substandard QoL. Interventions to improve self-esteem and social interactions might use QoL outcomes in evaluating effectiveness.     

Drug treatment of epilepsy: when does it fail and how to optimize its use?

Although modern community-based studies have shown that a majority of people with newly diagnosed epilepsy will enter long-term remission, seizures remain refractory to treatment in a substantial proportion of this population--perhaps as much as 40%. A consensus is being reached that, for operational purposes, pharmacoresistance can be suspected when two appropriately chosen, well-tolerated, first-line antiepileptic drugs (AEDs) or one monotherapy and one combination regimen have failed due to lack of efficacy. Poor prognostic factors include lack of response to the first AED, specific syndromes, symptomatic etiology, family history of epilepsy, psychiatric comorbidity, and high frequency of seizures. These observations suggest that prognosis can often be determined early in the course of the disorder. We propose a management paradigm that aims to maximize the chance of successful AED therapy, including the early use of "rational polytherapy" for patients not responding to monotherapy, and to identify efficiently patients suitable for "curative" resective surgery, in particular those with mesial temporal lobe epilepsy. An orderly approach to each epilepsy syndrome will optimize the chance of perfect seizure control and help more patients achieve a fulfilling life.     

Coordination changes in the early stages of learning to cascade juggle

The experiment was setup to examine the coordination changes in assembling the movement form of 3-ball cascade juggling. Eight adult participants learned to juggle over 4 weeks of practice. Juggling scores were recorded at each session and performance was videotaped at eight selected sessions for purposes of movement analysis. Once the basic spatial and temporal constraints on cascade juggling were satisfied, and the figure-8 juggling mode was established, temporal modulations of the relative motions of the hands were emphasized. All participants learned to juggle and the increase over practice in the number of consecutive balls caught was best fit with a power law. The non-proportional rate of performance increment was consistent with the qualitative changes in the form of the hand and ball movement kinematics that occurred over practice.     

Do college students drink more than their non-college-attending peers? Evidence from a population-based longitudinal female twin study

The association of college attendance with alcohol use and alcohol use disorders was examined in a population-based young adult female twin sample identified from a systematic search of birth records. College-attending women consumed a larger overall volume of alcohol than did their non-college-attending peers, but they were not more likely to be diagnosed with an alcohol use disorder. Significant associations between college attendance and alcohol involvement were probed using 3 different complementary research designs: multivariate cross-sectional analyses, longitudinal analyses of the precollege and college years, and cotwin-control analyses of twin pairs discordant for attending college. Although demographic and lifestyle characteristics accounted for most or all of the association between college attendance and alcohol involvement, there was 1 aspect of drinking behavior, occasionally consuming large quantities of alcohol, that remained significantly associated with college attendance even after controlling for these characteristics or for genetic and family background factors. These results are consistent with the conclusion that some aspect of the college experience may be an important environmental risk factor for this pattern of drinking among young adults.     

Psychopathy and physiological response to emotionally evocative sounds

Despite considerable evidence that psychopathic criminals are deviant in their emotional reactions, few studies have examined responses to both pleasurable and aversive stimuli or assessed the role of different facets of psychopathy in affective deviations. This study investigated physiological reactions to emotional sounds in prisoners selected according to scores on the 2 factors of Hare's Psychopathy Checklist--Revised (PCL-R; R. D. Hare, 1991). Offenders high on the PCL-R emotional-interpersonal factor, regardless of scores on the social deviance factor, showed diminished skin conductance responses to both pleasant and unpleasant sounds, suggesting a deficit in the action mobilization component of emotional response. Offenders who scored high only on the social deviance factor showed a delay in heart rate differentiation between affective and neutral sounds. These findings indicate abnormal reactivity to both positive and negative emotional stimuli in psychopathic individuals, and suggest differing roles for the 2 facets of psychopathy in affective processing deviations.     

MMPI-2 profile code types and measurement error

We studied simulated MMPI-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989) code type stability and change expected with measurement error for 12 MMPI-2 well-defined mean code type profiles. Profile scores for the 2 scales defining the code type were systematically varied to represent target code type profiles at 9 different levels of T-score profile definition. We randomly generated samples of 50 simulated, estimated true score profiles at each level of profile definition for each code type around the estimated true scores for each scale at each level of profile definition. Two sets of simulated profiles were developed. The first simulation was based on the reported means, test-retest reliabilities, and the standard errors of measurement for the MMPI-2 normative group. The second simulation was based on the means, standard deviations, and estimated retest stability for a clinical group of psychiatric patients. We calculated frequencies and percentages of simulated profiles with the highest estimated true scores on the same 2 scales as the original code type profile. Percentages of simulated profiles with the same 2 highest scales as the original code type profiles increased from 27% to 37% for the 3-point level of definition, 37% to 49% for the 5-point definition, 46% to 61% for 7-point definition, 63% to 78% for 10-point definition, 78% to 89% for 13-point definition, 83% to 93% for 15-point definition, and greater than 90% for profile definition greater than 15 points.     

The developmental ecology of urban males' youth violence

Data from a longitudinal study of 294 African American and Latino adolescent boys and their caregivers living in poor urban communities were used to test a developmental-ecological model of violence. Six annual waves of data were applied to evaluate the relations between microsystem influences of parenting and peer deviance (peer violence and gang membership), macrosystem influences of community structural characteristics and neighborhood social organization, and individual involvement in violence (level and growth). Structural equation modeling analyses showed that community structural characteristics significantly predicted neighborhood social processes. Parenting practices partially mediated the relation between neighborhood social processes and gang membership. Parenting practices was fully mediated in its relation to peer violence by gang membership. Gang membership was partially mediated by peer violence level in its relation to individual violence level. Although the overall set of relations does not satisfy mediation requirements fully in all instances, the model was validated for the most part, supporting a focus on a multilevel ecological model of influences on risk development.     

Do age of onset and course of illness define biologically distinct groups within atypical depression?

Illness course separates patients with atypical depression into tricyclic responders and nonresponders as does perceptual asymmetry. The authors therefore investigated whether the course-of-illness parameters would define groups within atypical depression differing in brain laterality. Patients with atypical depression were assessed for illness course and brain laterality. Two patient groups were defined, 1 with onset prior to age 20 plus a very chronic course, and a 2nd group having later onset or less chronic illness. Patients reporting early onset of very chronic dysphoria showed significantly less right-ear (left-hemisphere) accuracy and also differed in characteristic perceptual asymmetry when compared to patients with later onset or less chronicity. Course of illness may usefully define more homogeneous depressive subgroups within atypical depression.     

The use of latent trajectory models in psychopathology research

Despite the recent surge in the development of powerful modeling strategies to test questions about individual differences in stability and change over time, these methods are not currently widely used in psychopathology research. In an attempt to further the dissemination of these new methods, the authors present a pedagogical introduction to the structural equation modeling based latent trajectory model, or LTM. They review several different types of LTMs, discuss matching an optimal LTM to a given question of interest, and highlight several issues that might be particularly salient for research in psychopathology. The authors augment each section with a review of published applications of these methods in psychopathology-related research to demonstrate the implementation and interpretation of LTMs in practice.