Determinants of sexual and dating behaviors among adolescents.

Data on sexual behavior were obtained from 183 male and 193 female 12–18 yr olds, selected from 3 birth cohorts using a stratified random sample. Eight latent constructs—sexual and dating involvement, self-acceptance, feminist sex-role attitudes, deviant social network, importance of dating, lack of heterosexual competence, sexually active social network, and stressful change events—were hypothesized to explain the variance in 26 observed variables. Several causal models were tested that specified structural relationships among the latent constructs. A theoretically meaningful model was arrived at that linked the 8 error-free factors. This model indicates that dating and sexual involvement was a direct function only of the importance of dating, which in turn was positively related to self-acceptance and stressful changes and negatively related to lack of heterosexual competence. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An overview of Markov chain methods for the study of stage-sequential developmental processes.

This article presents an overview of quantitative methodologies for the study of stage-sequential development based on extensions of Markov chain modeling. Four methods are presented that exemplify the flexibility of this approach: the manifest Markov model, the latent Markov model, latent transition analysis, and the mixture latent Markov model. A special case of the mixture latent Markov model, the so-called mover-stayer model, is used in this study. Unconditional and conditional models are estimated for the manifest Markov model and the latent Markov model, where the conditional models include a measure of poverty status. Issues of model specification, estimation, and testing using the Mplus software environment are briefly discussed, and the Mplus input syntax is provided. The author applies these 4 methods to a single example of stage-sequential development in reading competency in the early school years, using data from the Early Childhood Longitudinal Study--Kindergarten Cohort. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Longitudinal adjustment patterns of boys and girls experiencing early, middle, and late sexual intercourse.

This study examined the association between psychosocial development and the timing of first sexual intercourse in a sample of White, rural adolescents. Two theoretical models were tested. The first model, derived from problem behavior theory proposed that earlier timing of first sexual intercourse is associated with longitudinal patterns of transition proneness and poor psychosocial adjustment. The second model, the stage termination model, proposed that early first sexual intercourse interferes with subsequent development, thereby resulting in negative developmental outcomes. Problem behavior theory was supported. For both boys and girls, earlier timing of first sexual intercourse was associated with longitudinal patterns of greater transition proneness and poorer psychosocial adjustment The stage termination model was not supported. No evidence was found suggesting that early timing of first sexual intercourse results in negative psychosocial outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of changing sexual activity on HIV prevalence

In a one-sex preferred mixing model, reductions in the rate of partner change by those with low sexual activity increase the average probability of HIV infection in the remaining pool of available partners. This increases prevalence among people with high activity, and since high activity people disproportionately influence the spread of HIV, may increase long-run prevalence in the population as a whole. Calculations using the model and survey data on sexual activity indicate that in low prevalence populations, many people have low enough activity that reductions in their activity might increase the endemic steady-state prevalance. If these results prove robust in more realistic models, they would support the case for targeting public health messages urging reduced sexual activity to high activity people.     

Full 1H NMR assignment of a 24-nucleotide RNA hairpin: application of the 1H 3D-NOE/2QC experiment

A mixed general linear model analysis of the development of sleep-wake states was conducted on 37 high-risk preterm infants and replicated with a second cohort of 34 infants. Most dependent variables showed significant development over the preterm period: active sleep decreased, and active waking, quiet waking, and the organization of active sleep and quiet sleep increased over the preterm period in both cohorts. The amount of quiet sleep also increased over age, but this change was significant only for Cohort 1. Seven infant characteristics used as covariates had only minor effects. There were no significant differences in the developmental trajectories (slopes) of the two cohorts. The amounts of four variables differed between cohorts: Cohort 2 infants had less sleep-wake transition, more active sleep, less active sleep without REM, and more regular quiet sleep. These findings suggest that developmental patterns of sleep wake states are stable enough in the preterm period that deviant individual patterns might be used to identify infants with neurological problems.     

Patterns of sexual and injecting risk behaviours in French intravenous drug users not reporting HIV and hepatitis C virus seropositivities

AIMS: To characterize and identify determinants of risk behaviour patterns of intravenous drug users (IDUs) independently of changes due to knowledge of HIV or hepatitis C Virus (HCV) seropositivity. DESIGN: A cross-sectional survey using a structured questionnaire concerning sexual, injecting and HIV and HCV antibody testing practices. SETTING: IDUs were interviewed in the Paris region at 10 treatment or psychosocial centres. PARTICIPANTS: Six hundred and twelve consecutive sexually active IDUs over 18 years able to answer the questionnaire. MEASUREMENTS: Five hundred and ninety-five IDUs completed the questionnaire. The risk-behaviour patterns of the 328 IDUs not reporting HIV or HCV seropositivity were analysed by phi correlation. Risk factors for each risk behaviour were determined by regression logistic models yielding odds ratios (OR) and their 95% confidence intervals (95% CI). FINDINGS: Several risk behaviour patterns were suggested: (1) lending, borrowing; (2) not or inconsistently testing HIV and HCV serology and not or inconsistently using condoms; (3) having multiple partners and prostitution; and (4) not using clean equipment. Alcohol abuse was independently and specifically associated with lending (OR = 3.8; 95% CI: 2.1-7.0) and borrowing (OR = 3.3; 95% CI: 1.8-6.1); homelessness with injecting risk behaviours and with prostitution (OR = 2.7; 95% CI: 1.2-6.1); low educational level and having children with not or inconsistently using condom and serology testing; and cocaine use with not or inconsistently using condoms (OR = 0.4; 95% CI: 0.3-0.7) and serology testing and not using clean equipment (OR = 0.4; 95% CI: 0.2-0.8). Having multiple partners and prostitution had no common risk factors. CONCLUSIONS: Identifying specific risk factors could help to target drug harm reduction programmes for each risk behaviour pattern among IDUs not reporting HIV and HCV seropositivity.     

The spread of HIV in Greenland. Heterosexual epidemic--risk or reality? A 10-year review of HIV transmission and preventive care

With the first report of an HIV-positive Inuit in 1985 Greenland was considered a high risk area for a self-sustained heterosexual HIV-epidemic, due to high incidences of sexually transmitted diseases. In 1986 a national HIV-intervention programme began with two major aims: Firstly, improved STD treatment and incitation to change of sexual high-risk behaviour, secondly, close monitoring of HIV-antibody test activity, partner notification and repeated surveys of knowledge and sexual behaviour in selected populations. Very early the spread of HIV in Greenland became heterosexually transmitted and self-sustained, with repeated local small-scale epidemics in a subpopulation characterized by frequent STD's, alcoholism, lack of education and vulnerable social and economic resources. From 1994 to 1997 a marked increase in new cases was reported, and in November 1997 the total number was 76 HIV-positives in the Greenlandic population of 50,000 Inuits. The successful defeat of STD's, such as gonorrhoea and syphilis has not been followed by a change in sexual behaviour among the youth in Greenland. High incidences of genital chlamydial infections, early sexual debut and high frequencies of excessive promiscuity render Greenland an alarming potential for a future HIV-epidemic. This threat calls for an intensified national prevention programme, with close monitoring of the known HIV-positives and the potentially infected persons in the population at risk, and new campaigns to reduce high-risk sexual behaviour among the youth.     

A Latent Markov Model for the Analysis of Longitudinal Data Collected in Continuous Time: States, Durations, and Transitions.

Markov models provide a general framework for analyzing and interpreting time dependencies in psychological applications. Recent work extended Markov models to the case of latent states because frequently psychological states are not directly observable and subject to measurement error. This article presents a further generalization of latent Markov models to allow for the analysis of rating data that are collected at arbitrary points in time. This extension offers new ways of investigating change processes by focusing explicitly on the durations that are spent in latent states. In an experience sampling application the author shows that such duration analyses can provide valuable insights about chronometric features of emotions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does age play a role in structure of anxiety and depression in children and youths? An investigation of the tripartite model in three age cohorts.

Although previous studies provide some support for a tripartite model of relations between anxiety and depression in children, there is evidence to suggest that anxiety and depression may be increasingly differentiated over development. Using a confirmatory factor analytic strategy with rationally selected item sets from the Revised Children's Manifest Anxiety Scale and the Children's Depression Inventory, the current study sought to test unitary, dual. and tripartite models for anxiety and depression in a cross-sectional design using 3 narrow-band age cohorts of nonreferred children and youths. The results found little evidence of increasing differentiation. All models provided a moderate fit to the data, with some evidence that a correlated 3-factor model was the preferred model in all age cohorts. Further research is required to explore the discriminant validity and clinical utility of the tripartite dimensions in childhood populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Generalized linear mixed models in dairy cattle breeding

Fitness and fertility traits of dairy cattle are of increasing importance and are often measured on a discrete scale. The development and application of generalized linear mixed models to the genetic analysis of these traits are reviewed. Because current genetic evaluation systems are predominantly based on animal models, the inferential challenges of highly parameterized generalized linear mixed models are discussed. Development and adoption of new methods for drawing appropriate inferences on dispersion parameters are essential. Recent hierarchical extensions have been proposed for generalized linear mixed models, allowing for complex dispersion patterns that accommodate heteroscedasticity and outlier robustness. Steady advances in available computing power have facilitated multiple-trait analyses involving continuous and discrete measures. Full Bayesian inference via the development of Markov Chain Monte Carlo methods will continue to allow even greater generality and dimensions in the genetic model.     

A person-centered, longitudinal approach to sexual victimization.

Objective: Little research has drawn attention to distinct patterns of sexual victimization across time, although previous findings strongly indicate heterogeneity. Using longitudinal data, we tested a series of latent class growth models in an attempt to find meaningful patterns of sexual victimization frequency among female college students. Method: A sample of women (n = 1,580) answered questions at 5 time points concerning their childhood, adolescent, and collegiate sexual experiences. Latent class growth analysis was used with frequencies of sexual victimization at each of the 5 time points as indicators. Results: A 4-class model was selected on the basis of its fit to the data and its interpretability. The 4 classes are interpreted as low/none, moderate-increasing, decreasing, and high-increasing trajectories of sexual victimization. Negative childhood experiences—childhood sexual abuse, witnessing domestic violence, and parental physical punishment—partially explained latent trajectory membership. Conclusion: Possible implications of this research include the development of more specialized primary, secondary, and tertiary sexual assault prevention programs based on the victimization trajectories indicated by these analyses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monthly measures of salivary testosterone predict sexual activity in adolescent males

Strong relationships between one-time serum testosterone (T) measures and sexual activity have been demonstrated in cross-sectional analyses of adolescent males. However, a subsequent longitudinal study of a separate adolescent sample, using semiannual plasma measures, failed to replicate cross-sectional findings. The present study reexamined the relationship between T and sexual activity using more frequently collected measures of salivary T and behavior. Saliva samples and weekly behavior checklists were collected over a 2-year period from the same panel sample of males on which semiannual analyses were based. Saliva samples representing measures approximately every fourth week of study participation were selected for T assay. The association between these monthly salivary T measures and weekly reports of incidents of sexual activity was assessed with repeated measures analyses. Higher levels of salivary T were significantly associated with an increasing hazard of coital initiation, and with more frequent coital and noncoital activity. Within-individual change analyses demonstrated that increases in salivary T were associated with increased sexual activity. Comparisons of models that varied specimen type, schedule of T measurement, and type of behavioral report indicated that all three factors contribute to the varying magnitude of hormone/behavior relationships that are demonstrated. These findings are consistent with a biosocial model of adolescent sexual development that pubertal changes in T are a causal factor in the timing of sexual initiation and the frequency of activity during adolescence.     

Bayesian Updating of Structural Models and Reliability using Markov Chain Monte Carlo Simulation

In a full Bayesian probabilistic framework for “robust” system identification, structural response predictions and performance reliability are updated using structural test data D by considering the predictions of a whole set of possible structural models that are weighted by their updated probability. This involves integrating h(θ)p(θ∣D) over the whole parameter space, where θ is a parameter vector defining each model within the set of possible models of the structure, h(θ) is a model prediction of a response quantity of interest, and p(θ∣D) is the updated probability density for θ, which provides a measure of how plausible each model is given the data D. The evaluation of this integral is difficult because the dimension of the parameter space is usually too large for direct numerical integration and p(θ∣D) is concentrated in a small region in the parameter space and only known up to a scaling constant. An adaptive Markov chain Monte Carlo simulation approach is proposed to evaluate the desired integral that is based on the Metropolis-Hastings algorithm and a concept similar to simulated annealing. By carrying out a series of Markov chain simulations with limiting stationary distributions equal to a sequence of intermediate probability densities that converge on p(θ∣D), the region of concentration of p(θ∣D) is gradually portrayed. The Markov chain samples are used to estimate the desired integral by statistical averaging. The method is illustrated using simulated dynamic test data to update the robust response variance and reliability of a moment-resisting frame for two cases: one where the model is only locally identifiable based on the data and the other where it is unidentifiable.     

A unifying review of linear gaussian models

Factor analysis, principal component analysis, mixtures of gaussian clusters, vector quantization, Kalman filter models, and hidden Markov models can all be unified as variations of unsupervised learning under a single basic generative model. This is achieved by collecting together disparate observations and derivations made by many previous authors and introducing a new way of linking discrete and continuous state models using a simple nonlinearity. Through the use of other nonlinearities, we show how independent component analysis is also a variation of the same basic generative model. We show that factor analysis and mixtures of gaussians can be implemented in autoencoder neural networks and learned using squared error plus the same regularization term. We introduce a new model for static data, known as sensible principal component analysis, as well as a novel concept of spatially adaptive observation noise. We also review some of the literature involving global and local mixtures of the basic models and provide pseudocode for inference and learning for all the basic models.     

Prospective use of glycoprotein IIb/IIIa receptor blockers in the emergency department setting

OBJECTIVE: We examined whether alcohol consumption and problem drinking decreased with age or if the reported declines were actually cohort and/or period effects. METHOD: We utilized data from the Normative Aging Study, assessing 1,267 men three times over an 18-year period (1973, 1982, 1991). Men were divided into five 9-year birth cohorts; age ranged from 46 to 72. RESULTS: Sequential analyses using repeated measures ANOVAs showed significant age, cohort and period effects. Although there was a tendency for alcohol consumption to decline with age, this was not true for all cohorts. Men born between 1910 and 1918 increased from an average of 350 to 440 drinks per year from their fifties to their sixties. The younger cohorts tended to report both more consumption and more problems. However, period had the most consistent effect in this study. There was an increase in problems and in consumption during the 1970s but a decrease in the 1980s, with the exception of the youngest cohort (1937-1945) who reported more problems in the 1991 assessment despite lower consumption. CONCLUSIONS: Age-related change in both consumption and problems varied depending upon which cohort or time period was assessed. Thus, drinking patterns are a complex amalgam of individual aging and societal change.     

Structural equation models of sexual harassment: Longitudinal explorations and cross-sectional generalizations.

Sexual harassment and its corresponding outcomes develop and change over time, yet research on this issue has been limited primarily to cross-sectional data. In this article, longitudinal models of harassment were proposed and empirically evaluated via structural equations modeling using data from 217 women who responded to a computerized questionnaire in 1994 and again in 1996. Results indicate that sexual harassment influences both proximal and distal work-related variables (e.g., job satisfaction, work withdrawal, job withdrawal) and psychological outcomes (e.g., life satisfaction, psychological well-being, distress). In addition, a replication of the L. F. Fitzgerald, F. Drasgow, C. L. Hulin, M. J. Gelfand, and V. J. Magley (1997) model of harassment was supported. This research was an initial attempt to develop integrated models of the dynamic effects of sexual harassment over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Change in sexual behaviour and decline in HIV infection among young pregnant women in urban Uganda

OBJECTIVE: To describe sexual behaviour that may partly explain a decline in HIV seroprevalence in pregnant women in urban settings in Uganda, East Africa. SETTINGS: Two major urban districts in Uganda. METHODS: Repeated population-based behavioural surveys in 1989 and 1995, and repeated HIV serological surveys in consecutive pregnant women attending antenatal clinics from 1989 to 1995. RESULTS: During the study period, a 2-year delay in the onset of sexual intercourse among youths aged 15-24 years and a 9% decrease in casual sex in the past year in male youths aged 15-24 years were reported. Men and women reported a 40% and 30% increase in experience of condom use, respectively. In the same study area, over the same period, there was an overall 40% decline in the rates of HIV seroprevalence among pregnant women attending antenatal clinics. It can be hypothesized that the observed declining trends in HIV correspond to a change in sexual behaviour and condom use, especially among youths. CONCLUSIONS: This is the first report of a change over a period of 6 years in male and female sexual behaviour, assessed at the population level, that may partly explain the observed decline in HIV seroprevalence in young pregnant women in urban Uganda. This result should encourage AIDS control programmes to pursue their prevention activities.     

Sexual issues and condom use among injecting drug users

Recent surveys of injecting drug users reveal that their injecting behaviours have changed in the light of HIV, but their sexual behaviours have not and, in particular, they remain reluctant to use condoms to reduce the risks of sexual transmission. In an attempt to explore this issue further the present study assessed the behaviours and attitudes of injecting drug users to sexual issues, including condom use. Condom use was low. Obstacles to their use included for some a desire to conceive, for many a belief in their infertility, a perceived invulnerability to HIV infection through their sexual behaviour patterns, a dislike of condoms and difficulty in negotiating condom use with partners. The lifestyle of drug users may also have an influence on condom use. Many drug users funded their habit through illegal activities including prostitution, theft and fraud. The association between these and other factors and condom use are explored.     

Epidemics of syphilis in the Russian Federation: trends, origins, and priorities for control

After continuous decline throughout the 1980s, surveillance-defined estimates of the incidence of syphilis in Russia have shown a rapid and substantial increase during the 1990s. The reasons for this epidemic are unclear, but must be sought among changes both in sexual behaviour and in the patterns of provision, use, and effectiveness of diagnostic, treatment, and contact tracing services. High incidence of sexually transmitted disease causes correspondingly high levels of morbidity and suffering as well as significant health-care and other economic costs. Our current understanding suggests that the transmissibility of HIV is increased by infection with sexually transmitted disease. The syphilis epidemic together with changes in sexual behaviour, increased travel and migration, and rapid increases in injecting drug use may create the conditions for an epidemic of sexually acquired HIV infection in Russia that substantially outstrips those encountered in most Western European countries.     

Modelling risk from a disease in time and space

This paper combines existing models for longitudinal and spatial data in a hierarchical Bayesian framework, with particular emphasis on the role of time- and space-varying covariate effects. Data analysis is implemented via Markov chain Monte Carlo methods. The methodology is illustrated by a tentative re-analysis of Ohio lung cancer data 1968-1988. Two approaches that adjust for unmeasured spatial covariates, particularly tobacco consumption, are described. The first includes random effects in the model to account for unobserved heterogeneity; the second adds a simple urbanization measure as a surrogate for smoking behaviour. The Ohio data set has been of particular interest because of the suggestion that a nuclear facility in the southwest of the state may have caused increased levels of lung cancer there. However, we contend here that the data are inadequate for a proper investigation of this issue.