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Curve Models (curve + models)
Selected AbstractsLatent Curve Models: a Structural Equation PerspectiveJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2008Cedric E. Ginestet No abstract is available for this article. [source] Adolescent smoking and depression: evidence for self-medication and peer smoking mediationADDICTION, Issue 10 2009Janet Audrain-McGovern ABSTRACT Aims The nature of the relationship between adolescent smoking and depression is unclear and the mechanisms that account for the comorbidity have received little investigation. The present study sought to clarify the temporal precedence for smoking and depression and to determine whether these variables are linked indirectly through peer smoking. Participants The sample was composed of 1093 adolescents participating in a longitudinal study of the behavioral predictors of smoking adoption. Design and measurements In this prospective cohort study, smoking, depression, peer smoking and other covariates were measured annually from mid-adolescence (9th grade; age 14) to late adolescence (12th grade, age 18). Findings Parallel processes latent growth curve models supported a bidirectional relationship between adolescent smoking and depression, where higher depression symptoms in mid-adolescence (age 14) predicted adolescent smoking progression from mid- to late adolescence (ages 14,18). A significant indirect effect indicated that higher depression symptoms across time predicted an increase in the number of smoking peers, which in turn predicted smoking progression from mid-adolescence to late adolescence. In addition, smoking progression predicted a deceleration of depression symptoms from mid- to late adolescence. A significant indirect effect indicated that greater smoking at baseline predicted a deceleration in the number of smoking peers across time, which predicted a deceleration in depression symptoms from mid-adolescence to late adolescence. Conclusions The current study provides the first evidence of bidirectional self-medication processes in the relationship between adolescent smoking and depression and highlights peer smoking as one explanation for the comorbidity. [source] Individual trajectories of substance use in lesbian, gay and bisexual youth and heterosexual youthADDICTION, Issue 6 2009Michael P. Marshal ABSTRACT Aims Several decades of research have shown that lesbian, gay and bisexual (LGB) adults are at high risk for substance use and substance use disorders, and a recent meta-analysis shows that these disparities most probably begin in adolescence; however, no studies to date have examined longitudinal growth in substance use in LGB youth and heterosexual youth to determine if they follow different trajectories into young adulthood. The primary aims of this paper were to estimate individual trajectories of substance use in youth and examine differences between self-identified LGB and heterosexual subsamples. Method A school-based, longitudinal study of health-related behaviors of adolescents and their outcomes in young adulthood was used to test our hypotheses (The National Longitudinal Study of Adolescent Health). Participants were included if they were interviewed at all three waves and were not missing information regarding self-identified sexual orientation (n = 10 670). Results Latent curve models (LCMs) showed that LGB identity was associated significantly with individual variability in substance use intercepts and slopes, above and beyond age, race and gender. Self-identified LGB youth reported higher initial rates of substance use and on average their substance use increased over time more rapidly than did substance use by heterosexual youth. Two other indicators of sexual orientation (same-sex romantic attraction and same-sex sexual behavior) were also associated with substance use trajectories, and differential results were found for youth who identified as ,mostly heterosexual' and bisexual compared with youth who identified as completely heterosexual or homosexual. Conclusions Sexual orientation is an important risk marker for growth in adolescent substance use, and the disparity between LGB and heterosexual adolescents increases as they transition into young adulthood. More research is needed in order to examine: causal mechanisms, protective factors, important age-related trends (using a cohort-sequential design), the influence of gay-related developmental milestones, curvilinear effects over time and long-term health outcomes. [source] Growth curve models for stochastic modeling and analyzing of natural disinfection of wastewaterENVIRONMETRICS, Issue 8 2006Wolfgang Bischoff Abstract This work is motivated by a study on the natural disinfection of wastewater in marine environment for ocean outfall systems without chlorination. In the study of the disinfection on wastewater in marine environment two natural factors, consisting of light intensity and salinity, one controllable factor, the volumetric mixing ratio of seawater to wastewater, and one random effect factor, the existence of predators, were investigated. Our problem and data are modeled by a growth curve model with an unknown random parameter that can be described by a mixed model with the factors mentioned above as covariates. For our model we determine the optimal variance estimations. Finally, we apply our model with these optimal estimated variance components to the data obtained from the real experiments. Copyright © 2006 John Wiley & Sons, Ltd. [source] Growth in women's political representation: A longitudinal exploration of democracy, electoral system and gender quotasEUROPEAN JOURNAL OF POLITICAL RESEARCH, Issue 1 2010PAMELA PAXTON The expansion of women's formal political representation ranks among the most significant trends in international politics of the last 100 years. Though women made steady political progress, substantial country-level variation exists in patterns of growth and change. In this article, longitudinal theories are developed to examine how political factors affect women's political representation over time. Latent growth curve models are used to assess the growth of women in politics in 110 countries from 1975 to 2000. The article investigates how electoral systems, national-level gender quotas and growth of democracy , both political rights and civil liberties , impact country-level trajectories of women's legislative representation. It is found: first, national quotas do affect women's political presence, but at a lower level than legislated by law; second, the impact of a proportional representation system on women's political representation is steady over time; and third, democracy, especially civil liberties, does not affect the level of women's political representation in the earliest period, but does influence the growth of women's political representation over time. These findings both reinforce and challenge prior cross-sectional models of women's political representation. [source] Rational Choice and Developmental Influences on Recidivism Among Adolescent Felony OffendersJOURNAL OF EMPIRICAL LEGAL STUDIES, Issue 4 2007Jeffrey Fagan Recent case law and social science both have claimed that the developmental limitations of adolescents affect their capacity for control and decision making with respect to crime, diminishing their culpability and reducing their exposure to punishment. Social science has focused on two concurrent adolescent developmental influences: the internalization of legal rules and norms that regulate social and antisocial behaviors, and the development of rationality to frame behavioral choices and decisions. The interaction of these two developmental processes, and the identification of one domain of socialization and development as the primary source of motivation or restraint in adolescence, is the focus of this article. Accordingly, we combine rational choice and legal socialization frameworks into an integrated, developmental model of criminality. We test this framework in a large sample of adolescent felony offenders who have been interviewed at six-month intervals for two years. Using hierarchical and growth curve models, we show that both legal socialization and rational choice factors influence patterns of criminal offending over time. When punishment risks and costs are salient, crime rates are lower over time. We show that procedural justice is a significant antecedent of legal socialization, but not of rational choice. We also show that both mental health and developmental maturity moderate the effects of perceived crime risks and costs on criminal offending. [source] Whatever Happened to Goldilocks?OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 1 2006The Role of Expectations in Estimates of the NAIRU in the US, the UK Abstract During the second half of the 1990s the US economy was characterized as the Goldilocks economy: not too hot, nor too cold, but just right. It was argued that this represented a new paradigm, enabling unemployment to remain low without igniting inflationary pressure. We examine the evidence for a change in the relationship between inflation and unemployment for the US and UK using Phillips curve models. The impact of including explicit inflation expectations is also considered. Inflation expectations are found to play an important role, particularly in the US. When expectations are included there is still evidence that the non-accelerating inflation rate of unemployment (NAIRU) steadily declined during the late 1990s, although this decline in the US NAIRU is not found solely in the 1990s. [source] Functional Mixed Effects ModelsBIOMETRICS, Issue 1 2002Wensheng Guo Summary. In this article, a new class of functional models in which smoothing splines are used to model fixed effects as well as random effects is introduced. The linear mixed effects models are extended to non-parametric mixed effects models by introducing functional random effects, which are modeled as realizations of zero-mean stochastic processes. The fixed functional effects and the random functional effects are modeled in the same functional space, which guarantee the population-average and subject-specific curves have the same smoothness property. These models inherit the flexibility of the linear mixed effects models in handling complex designs and correlation structures, can include continuous covariates as well as dummy factors in both the fixed or random design matrices, and include the nested curves models as special cases. Two estimation procedures are proposed. The first estimation procedure exploits the connection between linear mixed effects models and smoothing splines and can be fitted using existing software. The second procedure is a sequential estimation procedure using Kalman filtering. This algorithm avoids inversion of large dimensional matrices and therefore can be applied to large data sets. A generalized maximum likelihood (GML) ratio test is proposed for inference and model selection. An application to comparison of cortisol profiles is used as an illustration. [source] | ||||||||||