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PubMed2004

Differential contribution of parents and friends to smoking trajectories during adolescence.

The purpose of this study was to assess the relative contribution of friends' and parents' smoking on the age of smoking initiation. A sample of 812 preadolescents, who were part of an accelerated longitudinal design, participated in the study over a 4-year period. Three smoking trajectory groups were first established: an age 11-12 starters group (5.7% of the sample), an age 12-13 starters group (11.1% of the sample), and an age 13-14 starters group (7.9% of the sample). A fourth trajectory group included the children who had not started smoking by age 15 years and who represented the majority of the participants (75.4%). After controlling for parental education, gender, and participants' behavioral and academic maladjustment, a series of logistic regressions revealed that parents' smoking assessed during the same year predicted membership in the age 11-12 starters trajectory group. Both parents' and friends' smoking predicted membership in the age 12-13 starters group. Finally, only friends' smoking predicted membership in the age 13-14 starters group. The results are discussed in light of the controversy about the contribution of parents' and friends' smoking behavior to smoking initiation in adolescents.

Adolescent↗
PubMed2006

Developmental trajectories of adolescent popularity: a growth curve modelling analysis.

Growth curve modelling was used to examine developmental trajectories of sociometric and perceived popularity across eight years in adolescence, and the effects of gender, overt aggression, and relational aggression on these trajectories. Participants were 303 initially popular students (167 girls, 136 boys) for whom sociometric data were available in Grades 5-12. The popularity and aggression constructs were stable but non-overlapping developmental dimensions. Growth curve models were run with SAS MIXED in the framework of the multilevel model for change [Singer, J. D., & Willett, J. B. (2003). Applied longitudinal data analysis. Oxford, UK: Oxford University Press]. Sociometric popularity showed a linear change trajectory; perceived popularity showed nonlinear change. Overt aggression predicted low sociometric popularity but an increase in perceived popularity in the second half of the study. Relational aggression predicted a decrease in sociometric popularity, especially for girls, and continued high-perceived popularity for both genders. The effect of relational aggression on perceived popularity was the strongest around the transition from middle to high school. The importance of growth curve models for understanding adolescent social development was discussed, as well as specific issues and challenges of growth curve analyses with sociometric data.

Adolescent↗
PubMed2004

Racial differences in trajectories of cigarette use.

This study examined racial differences in developmental trajectories of cigarette smoking from childhood into young adulthood. We used data from the Pittsburgh Youth Study, a prospective, longitudinal study of high-risk males. We developed trajectories of cigarette smoking from age 10 through age 25. Models were estimated separately for African-Americans (N = 562) and Whites (N = 421) because preliminary analyses indicated that there were significant racial differences in onset, levels and patterns of cigarette use. Three trajectory groups emerged for both races: nonsmokers, light/occasional smokers and heavy/regular smokers. Significantly more Whites were in the heavy/regular smoker group and more African-Americans were in the nonsmoker group. White compared to African-American heavy/regular smokers began smoking earlier and reached higher mean quantities of cigarettes per day. In addition, there were racial differences in the timing and rapidity of the development of regular smoking over time. Race remained a significant predictor of cigarette use even after controls for socioeconomic status. Overall, the results indicate that developmental trends in smoking differ by race and that cigarette smoking remains more prevalent and more frequent for White than African-American males, at least through young adulthood.

Adolescent↗
PubMed2006

Toward a trajectory of identity reconstruction in chronic fatigue syndrome/myalgic encephalomyelitis: a longitudinal qualitative study.

BACKGROUND: Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is an illness associated with high levels of physical and cognitive disability over a prolonged period of time. Recovery from CFS/ME can be interspersed with relapses. Further, the legitimacy of the illness continues to be questioned within and beyond the health profession. AIM: This paper examines the reconstruction of self-identity for those experiencing CFS/ME. METHOD: This longitudinal qualitative study involved up to three in-depth interviews with 17 people with CFS/ME and family members. RESULTS: A trajectory that describes transitions in identity over time and the range of elements that influence these is proposed. During the acute phase of illness, characterised by total debility, people adopted the traditional sick role. The medium term phase highlighted movement between disability as part of the total self, total debility, and/or the adoption of a supernormal identity. The longer-term phase was defined for the majority of participants as the positive reconstruction of self. Identity was contingent with positive and negative experiences and responses co-existing with the potential to 'tip' the balance and perceived identity. In the longer term people's identity became more static with the development of coping strategies to maintain this. The trajectory can be described as pendular and movement between each type of identity was possible during all phases of the illness experience depending on the nature and impact of the illness and responses given to these. The proposed trajectory represents a dynamic model of identity reconstruction. CONCLUSION: Understanding the patients' experience and recognising that different stages may exist is important for health professionals. This awareness can enhance shared understanding and opportunities to work with people in negotiating the impact of illness.

Activities of Daily Living↗
PubMed2005

Examining differential effects of psychological treatment of depressive disorder: an application of trajectory analyses.

BACKGROUND: Although different psychological treatments of depression seem equally effective, studies in this area have not taken sufficient account of the heterogeneity among patients. Modern techniques for longitudinal data analysis can be helpful in examining differential effects of psychological interventions on specific subpopulations of patients. METHODS: Outpatients in mental health care, diagnosed with DSM-IV major depressive disorder, were randomly assigned to cognitive behavior therapy (N=199) or treatment as usual (N=226). Every 3 months for a total of 1.5 years, depressive symptomatology was measured using the SCL-90. Growth mixture modeling techniques were used to identify different trajectory classes of patients. The impact of type of treatment (treatment as usual vs. cognitive behavior therapy) was examined for each identified trajectory. RESULTS: On average, patients in both test conditions improved significantly from baseline to posttest, and no significant difference was found between the conditions. However, four different trajectory classes could be distinguished within the sample. Most patients were classified into the two classes with the lowest depression scores at baseline (31% and 33% of the total sample). For these two classes, no significant differences in the course of depressive symptoms were found between the two conditions. In the two classes with the more severe depression scores (10% and 26% of the sample), however, cognitive behavior therapy was significantly more effective than treatment as usual. CONCLUSIONS: Although different treatments may seem to be equally effective, this does not have to be true for all classes of patients. Longitudinal research on the treatment of mental disorders should take heterogeneity among patients into account.

Adult↗
PubMed2006

Ion trajectory simulation for electrode configurations with arbitrary geometries.

A multi-particle ion trajectory simulation program ITSIM 6.0 is described, which is capable of ion trajectory simulations for electrode configurations with arbitrary geometries. The electrode structures are input from a 3D drawing program AutoCAD and the electric field is calculated using a 3D field solver COMSOL. The program CreatePot acts as interface between the field solver and ITSIM 6.0. It converts the calculated electric field into a field array file readable by ITSIM 6.0 and ion trajectories are calculated by solving Newton's equation using Runge-Kutta integration methods. The accuracy of the field calculation is discussed for the ideal quadrupole ion trap in terms of applied mesh density. Electric fields of several different types of devices with 3D geometry are simulated, including ion transport through an ion optical system as a function of pressure. Ion spatial distributions, including the storage of positively charged ions only and simultaneous storage of positively/negatively charged ions in commercial linear ion traps with various geometries, are investigated using different trapping modes. Inelastic collisions and collision induced dissociation modeled using RRKM theory are studied, with emphasis on the fragmentation of n-butylbenzene inside an ideal quadrupole ion trap. The mass spectrum of 1,3-dichlorobenzene is simulated for the rectilinear ion trap device and good agreement is observed between the simulated and the experimental mass spectra. Collisional cooling using helium at different pressures is found to affect mass resolution in the rectilinear ion trap.

Journal Article↗
PubMed2006

Eye movement trajectories and what they tell us.

In the last two decades, research has shown that eye movement trajectories can be modified by situational determinants. These modifications can inform us about the mechanisms that control eye movements and they can yield information about the oculomotor, memory and attention system that is not easily obtained via other sources. Eye movement trajectories can deviate either towards or away from elements in the visual field. We review the conditions in which these deviations are found and the mechanisms underlying trajectory deviations. It is argued that deviations towards an element are caused by the unresolved competition in the oculomotor system between elements in a visual scene. Deviations away from an element are mainly observed in situations in which top-down preparation can influence the target selection process, but the exact cause of such deviations remains unclear.

Attention↗
PubMed2005

Logistic trajectory maps and aerosol mixing due to asynchronous flow at airway bifurcations.

Aerosols too large for significant Brownian transport, and too small for significant inertial transport, are nonetheless known to deposit deep in the lung, and are associated with increased risk of pulmonary disease. Classical models fail to explain such transport. We hypothesized that kinematic irreversibility in ventilation, arising from velocity saddle-points or from flow asynchrony at airway bifurcations, may be the fundamental transport mechanism. Our experimental evidence shows striking trajectory irreversibility in rat lungs ventilated with 2-color polymerizable silicones, representing resident and tidal gas. The striated patterns in small airways, even after one ventilatory cycle, support our hypothesis. Here we analyze bifurcating flow asynchrony in a simplified one-dimensional model. We find: unexpected richness and chaos in particle trajectories; almost all trajectories visit all spatial positions; surprisingly, there is complete mixing-the limiting concentration is spatially uniform. This is a new finding supporting the idea that kinematic irreversibility is a potent mixing and transport mechanism for aerosols deep in the lung.

Aerosols↗
PubMed2006

Consumption and costs of antihypertensive drugs in Mexico: are diuretic agents a standing technological trajectory?

BACKGROUND: Little is known about hypertension medication consumption and costs in Mexico. Hypertension control is a pharmacological challenge and a public health issue. OBJECTIVE: (a) To compare drug sales, number of written prescriptions, and monthly treatment costs among 5 classes of antihypertensive drugs and (b) to analyze diuretic drug sales and prescriptions to determine whether these antihypertensive agents represent an established technological trajectory. METHODS: A retrospective time series data study from 1999 to 2003. Data sources used were International Marketing Services of Mexico drug sales and the Mexico Prescription Audit databases. The 5 different classes of antihypertensive drugs were accommodated into 4 main technological trajectories according to their main biological mechanisms of action. Each technological trajectory was assessed using consumption and prescription data. Daily defined dose was used to calculate drug treatment costs. RESULTS: The market for cardiovascular agents is one of the largest, and in 2003 accounted for a value market share of 59 billion US dollar and a unit share of 40.7 million. Among cardiovascular agents, antihypertensive drugs made up a large percentage of market shares. Calcium channel blockers and angiotensin-converting enzyme inhibitors I had the biggest share value of the total cardiovascular market. Amlodipine had the highest share among calcium channel blockers, and enalapril and captopril had the largest share among angiotensin-converting enzyme inhibitors I. The top-selling diuretic drug was furosemide. The trend in number of prescriptions was parallel to that in sales. The diuretic spironolactone was the most expensive drug treatment (59 US dollar). Treatment with spironolactone might represent 47% of the income of a Mexican family if their household income was close to minimum wage (124 US dollar). CONCLUSIONS: The most effective and least expensive drugs-diuretics-had the smallest market share of all antihypertensive agents in Mexico. Nevertheless, diuretic agents are still in use and kept over time a steady market share both in value and in units.

Adrenergic beta-Antagonists↗
PubMed2005

Spatial and temporal aspects of oculomotor inhibition as revealed by saccade trajectories.

The spatial and temporal effect of distractor related inhibition on stimulus elicited (reflexive) and goal driven (voluntary) saccades, was examined using saccade trajectory deviations as a measure. Subjects made voluntary and reflexive saccades to a target location on the vertical midline, while the distance of a distractor from the target was systematically manipulated. The trajectory curvature of both voluntary and reflexive saccades was found to be subject to individual differences. Saccade curvature was found to decrease monotonically with increasing distractor distance from target for some subjects while for others no reduction in curvature or even an increase was found. These results could not be explained by latency differences or landing position effects. The different patterns of distractor effects on saccade trajectories suggest the additional influence of a non-spatial inhibitory mechanism.

Adult↗
PubMedDate not supplied

Cigarette smoking from adolescence to young adulthood: women's developmental trajectories and associates outcomes.

OBJECTIVES: This study aimed to compare 1,442 women with distinct developmental trajectories of smoking from ages 13-23 on important young adult outcomes at age 29 (e.g., education, income, mental and physical health, arrest history, drug and alcohol abuse), as well as early transitions to sexual intercourse, parenthood, and marriage. METHODS: Women were classified as Abstainers or into 1 of 5 trajectory classes for which they had the highest probability of membership: Stable Highs, Early Increasers, Late Increasers, Triers, and Decreasers. Regression analysis was used to model outcomes as a function of trajectory class membership. RESULTS: Abstainers and Triers generally had more favorable outcomes than Stable Highs and Early Increasers. Decreasers were more likely to graduate from college than Stable Highs and Early Increasers and had a lower arrest rate than Stable Highs. Women who increased their smoking from initial low levels (Late Increasers) generally had poorer young adult outcomes compared to Triers and Abstainers, but lower risk for early sex and early parenthood compared to Stable Highs and Early Increasers. CONCLUSIONS: Women with certain patterns of smoking from age 13-23 are at heightened risk for early transitions to sexual activity and parenthood, as well as health, behavioral, and socioeconomic problems during young adulthood.

Adolescent↗
PubMed2004

Smoking topography and trajectory of asthmatic adolescents requesting cessation treatment.

BACKGROUND: Teenage smokers cite health concerns as their primary motivators for tobacco smoking cessation. Smoke exposure aggravates the clinical course of asthma, yet few reports have examined the association between asthma and smoking topography and trajectory. METHODS: Before their enrollment in a smoking cessation trial, we assessed the smoking topography (i.e., puff volume, maximum puff velocity, puff duration, and interpuff interval) and smoking trajectory (i.e., age of first cigarette, age of daily smoking, time to treatment request, and prior quit attempts) in 30 self-reported asthmatic and 92 nonasthmatic tobacco-dependent teenagers (mean age, 15.2 +/- 1.3 years, 28.7% African-American). Approximately one-half of asthmatics used prescribed medications for their asthma. RESULTS: There was no significant difference in smoking topography or smoking trajectory variables between asthmatic and nonasthmatic adolescents, nor between medicated and nonmedicated asthma subgroups. CONCLUSIONS: Although tobacco smoking exacerbates asthmatic symptoms, these data suggest that age of smoking initiation, as well as smoking topography characteristics in asthmatic adolescents, does not differ from those of adolescents without asthma. These findings highlight the need for more effective health counseling of asthmatic youth regarding the physical and behavioral effects of smoking.

Adolescent↗
PubMed2002

Does representational momentum reflect a distortion of the length or the endpoint of a trajectory?

Observers viewed a moving target, and after the target vanished, indicated either the initial position or the final position of the target. In Experiment 1, an auditory tone cued observers to indicate either the initial position or the final position; in Experiment 2, different groups of observers indicated the initial position or the final position. Judgments of the initial position were displaced backward in the direction opposite to motion, and judgments of the final position were displaced forward in the direction of motion. The data suggest that the remembered trajectory is longer than the actual trajectory, and the displacement pattern is not consistent with the hypothesis that representational momentum results from a distortion of memory for the location of a trajectory.

Adult↗
PubMed2001

Improved sea ice parcel trajectories in the Arctic via data assimilation.

An assimilated sea ice motion product is used to track ice parcels in several regions of the Arctic over time periods of one day to several weeks during 1992-1993. Motions simulated using a two-dimensional, dynamic-thermodynamic sea ice model are combined with motions derived from daily 85 GHz special sensor microwave/imager (SSM/I) imagery using an optimal interpolation method that minimizes error covariance. Assimilation attenuates the tracking error over the stand-alone model in comparison to buoy trajectories with the same starting location and time. The average 14-day assimilated trajectory's displacement error is as much as 34% lower than the model trajectory, while the RMS direction error is decreased by up to 10 degrees (24%). Assimilation can also yield an estimate of dispersion, which is not retrievable by point buoy observations. An assimilation approach improves estimates of ice drift and has the potential to further the understanding of ice mass flux, freshwater flux, and pollutant transport in the polar regions.

Arctic Regions↗
PubMed2001

Back-trajectory analyses of fine particulate matter measured at Big Bend National Park in the historical database and the 1996 scoping study.

Analyses of the sources of fine particles associated with visibility reduction at Big Bend National Park during a 10-year period from 1989-1998 and from a regional visibility scoping study conducted during September and October 1996 at 19 sites in Texas and Mexico are summarized and compared. Fine sulfate particles are the largest fraction of the fine mass, and scattering by sulfates is estimated to be nearly half of the non-Rayleigh light extinction at Big Bend. Fine particulate sulfur concentrations are seasonal, with the highest values occurring during the summer and fall when back trajectory analyses show that air masses are most likely to arrive at Big Bend from the southeast after passing over Mexico or from areas to the northeast including east Texas. Episodically, high concentrations of fine mass and high light extinction values can be due to other species such as fine organic carbon or blowing soil dust. Organic carbon concentrations are often extremely high during the spring, especially during May. A combination of back trajectory analyses and the coincidence of high organic carbon and high non-soil potassium concentrations leads to the hypothesis that these concentrations are due to fires, primarily seasonal agricultural burning in Mexico and Central America. Fine soil concentrations often reach values that are twice the annual mean during July. These concentrations also frequently have high Al/Ca ratios, indicative of Saharan dust. Back trajectories associated with these events show air masses arriving from the southeast and are consistent with the hypothesis of transport of air masses from Africa during July. There is a high frequency of transport of air masses from Mexico to Big Bend, especially during the summer when fine mass concentrations and light extinction are highest. Therefore, sources and potential sources of sulfates and other fine particles in Mexico, particularly in areas southeast of the park have a high likelihood of contributing to visibility degradation at the park. Source areas to the northeast of the park, in east Texas and farther upwind also contribute to high fine sulfate concentrations.

Air Movements↗
PubMed2004

Diverse trajectories of cocaine use through early adulthood among rebellious and socially conforming youth.

This paper tests predictions of continuity and change in antisocial behavior over time as derived from population heterogeneity and life-course perspectives. These predictions are assessed with respect to a rarely studied form of delinquent/criminal behavior, cocaine use during the late-teenage and young adult years. We first examine the extent to which differential propensities toward antisocial behavior can be detected in a nationally representative sample of youth aged 14-16 in 1979. Based on self-reported delinquent and criminal activities in late adolescense, traditional cross-sectional latent-class analysis identifies three groups of antisocial/rebellious respondents and a group of non-offenders. We then follow these groups into early adulthood, examining age trajectories of cocaine usage between 1984 and 1998. Latent-class trajectory models identify clusters of respondents who show similar age trajectories of cocaine use over time and provide parameter estimates that predict membership in those clusters. In support of the population heterogeneity perspective, we find that antisocial/rebellious youth have higher probabilities of cocaine use throughout early adulthood than non-of-fending youth. There is, however, much variation in drug use patterns among the groups as they aged. In support of a life-course perspective, we find that social ties to schools, families, religion, and the labor market help differentiate youth who refrain from, maintain, or desist from using cocaine through early adulthood.

Antisocial Personality Disorder↗
PubMed2000

Continuity and change in women's weight orientations and lifestyle practices through pregnancy and the postpartum period: the influence of life course trajectories and transitional events.

The life course perspective offers a framework for understanding continuity and change in health and health practices. Body weight, and the diet and physical activity strategies used to manage weight in pregnancy and the postpartum period, are a focus of much study because of an association between parity and body weight. The motherhood transition offers an opportunity to study weight concerns and weight management strategies during a period of weight fluctuation that is part of a life transition for many women. Our aim was to develop an in-depth understanding of women's experiences of pregnancy and postpartum weight changes, the strategies that women used to deal with weight changes, and patterns in their attitudes and strategies across pregnancy and the postpartum period. A longitudinal design, using multiple, in-depth, qualitative interviews with 36 women from pregnancy through the postpartum period, was chosen for data collection. Prepregnancy orientations towards body weight emerged as the primary influence on women's pregnancy and postpartum attitudes towards weight, on patterns of physical activity and diet, and on postpartum weight outcomes among most study participants. Four different trajectories ("relaxed maintenance", "exercise", "determined", and "unhurried"), characterized by differences in women's orientations towards their body weight and their diet and physical activity patterns across pregnancy and the postpartum period, emerged from the data. Only a few women diverged from prepregnancy trajectories in weight orientation and diet and physical activity patterns postpartum. Delayed resumption of prepregnancy physical activity and dietary patterns contributed to postpartum weight retention for a subset of "exercisers". Stress and age- or role-related changes in perspective interrupted the continuity of weight orientations and behavioral patterns for three other women. These findings highlight the direction and momentum provided by trajectories in health attitudes and strategies as processes shaping responses to a life transition.

Adult↗
PubMed2000

Trajectory encoding in the hippocampus and entorhinal cortex.

We recorded from single neurons in the hippocampus and entorhinal cortex (EC) of rats to investigate the role of these structures in navigation and memory representation. Our results revealed two novel phenomena: first, many cells in CA1 and the EC fired at significantly different rates when the animal was in the same position depending on where the animal had come from or where it was going. Second, cells in deep layers of the EC, the targets of hippocampal outputs, appeared to represent the similarities between locations on spatially distinct trajectories through the environment. Our findings suggest that the hippocampus represents the animal's position in the context of a trajectory through space and that the EC represents regularities across different trajectories that could allow for generalization across experiences.

Algorithms↗