In this study, the authors focused on signs of early childhood misbehavior that might be linked t... more In this study, the authors focused on signs of early childhood misbehavior that might be linked to the risk of becoming tobacco-dependent. Standardized teacher ratings of misbehavior were obtained for an epidemiologic sample of first graders entering an urban mid-Atlantic public school system in 1985 and 1986. Fifteen years later, 1,692 of the students were reassessed (nearly 75% of the
In longitudinal behavioural studies, it is common to have multiple categorical indicators for mea... more In longitudinal behavioural studies, it is common to have multiple categorical indicators for measuring a theoretical construct of interest. A latent class model is presented that accounts for the structure in a set of correlated, categorical variables measured at discrete time periods, drawing information from these variables to form a smaller number of latent classes. The dependence of the resulting latent class model parameters on suspected factors over time is simultaneously modelled using a baseline-category logistic regression model. Estimation of the model parameters is achieved using an estimating equations procedure. A motivating example is provided from a longitudinal study of suspected linkages between monitoring or supervision by parents and the occurrence of drug use behaviours in an epidemiologic sample of school-attending youths.
The present study uses latent class methods and multiple regression to shed light on hypothesized... more The present study uses latent class methods and multiple regression to shed light on hypothesized cocaine dependence syndromes experienced by community residents, who initiated cocaine use within 24 months of survey assessment, and explores possible variation in risk. Identified within public use data files from the United States National Household Surveys on Drug Abuse (NHSDA), and with assessments completed between 1995 and 1998, the study sample consists of 927 recent-onset cocaine users, defined as having initiated cocaine use no more than 24 months prior to assessment (approximate median elapsed time since onset of use approximately 12-13 months). The NHSDA included items to assess seven clinical features often associated with cocaine dependence, which were used in latent class modeling. Empirically derived latent classes, in conjunction with prior theory, tend to support a three-class solution, according to which 4% of recent-onset users are members of a class that resembles the DSM-IV cocaine dependence syndrome (mean: 5.4 clinical features (CF)); 16% might be in a cocaine dependence prodrome (mean: 2.4 CF); 80% of recent-onset cocaine users had few or no clinical features (mean<1 CF). Results from latent class regressions indicate that susceptibility to rapid transition from first cocaine use to onset of the LCA-assigned cocaine dependence syndrome might depend upon whether the user starts smoking crack-cocaine and, independently, age at first cocaine use.
Journal of the Royal Statistical Society: Series A (Statistics in Society), 2000
Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder which is most of... more Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder which is most often diagnosed in childhood with symptoms often persisting into adulthood. Elevated rates of substance use disorders have been evidenced among those with ADHD, but recent research focusing on the relationship between subtypes of ADHD and specific drugs is inconsistent. We propose a latent transition model (LTM) to guide our understanding of how drug use progresses, in particular marijuana use, while accounting for the measurement error that is often found in self-reported substance use data. We extend the LTM to include a latent class predictor to represent empirically derived ADHD subtypes that do not rely on meeting specific diagnostic criteria. We begin by fitting two separate latent class analysis (LCA) models by using second-order estimating equations: a longitudinal LCA model to define stages of marijuana use, and a cross-sectional LCA model to define ADHD subtypes. The LTM model parameters describing the probability of transitioning between the LCA-defined stages of marijuana use and the influence of the LCA-defined ADHD subtypes on these transition rates are then estimated by using a set of first-order estimating equations given the LCA parameter estimates. A robust estimate of the LTM parameter variance that accounts for the variation due to the estimation of the two sets of LCA parameters is proposed. Solving three sets of estimating equations enables us to determine the underlying latent class structures independently of the model for the transition rates and simplifying assumptions about the correlation structure at each stage reduces the computational complexity.
An earlier study reported on the development of a scale to measure feeling states during acute bo... more An earlier study reported on the development of a scale to measure feeling states during acute bouts of exercise: the Exercise-induced Feeling Inventory (EFI-A). The present study reports on the psychometric properties of a revised scale to assess responses to habitual or chronic physical activity: the EFI-C. The EFI-C was administered during baseline testing to 830 sedentary men and women patients with a mean age of 51.5 years. Factor analytic procedures revealed that the EFI-C consisted of two factors, one assessing pleasant feeling states and a second that taps the unpleasant experience of physical exhaustion. Both subscales have excellent internal consistency reliability coefficients (~0.90) and are reasonably stable over time, having test-retest coefficients in excess of 0.70. The scales correlated in expected directions with related constructs and in preliminary analyses showed an anticipated pattern of sensitivity to physical activity interventions. Mean scores for various demographic groups are reported. Future research should examine whether the EFI-C is a predictor of adherence to physical activity and its potential role in mediating the positive mental health effects of physical activity.
This study describes diurnal variations in feeling states in 84 women as a function of involvemen... more This study describes diurnal variations in feeling states in 84 women as a function of involvement in physical activity. Women completed feeling state checklists before and after bouts of vigorous physical activity that lasted a minimum of 20 min and on a stratified random-sampling protocol in response to a stimulus from an electronic pager. Participants self-reported the date, the time of day, the stimulus for responding, their current feeling states, and their ongoing activity. A total of 7,295 complete mood and activity reports were recorded in response to pager calls that were further coded into experience samplings that occurred on a nonexercise day, prior to exercise on an exercise day, and following exercise on an exercise day. Multilevel modeling analyses showed that in samplings recorded following exercise on exercise days, positive engagement, revitalization, and tranquility were elevated in comparison with predicted diurnal patterns.
Few studies have examined correlates of heavy drinking among rural immigrant Latino men. This ana... more Few studies have examined correlates of heavy drinking among rural immigrant Latino men. This analysis identified correlates of typical week drunkenness and past 30-day heavy episodic drinking, within a sample of immigrant Latino men in rural North Carolina (n = 258). In the bivariate analyses, Mexican birth, entering the United States as an adult, and year-round employment were associated with increased odds of typical week drunkenness, and higher acculturation and affiliation with a religion with strict prohibitions against drinking alcohol were associated with lower odds of typical week drunkenness. Being older, Mexican birth, entering the United States as an adult, and lower acculturation were associated with increased odds of heavy episodic drinking, and affiliation with a religion with strict prohibitions against drinking alcohol and completing high school were associated with decreased odds of heavy episodic drinking. In multivariable modeling, only religious affiliation was associated with typical week drunkenness. Mexican birth, entering the United States as an adult, and lower acculturation were associated with increased odds of heavy episodic drinking, and affiliation with a religion with strict prohibitions against drinking alcohol and completing high school were associated with lower odds of heavy episodic drinking. The health of minority men in the United States has been neglected, and immigrant Latino men comprise a particularly vulnerable population. This analysis provides initial data on some factors associated with heavy drinking within a population about which little is known. Future studies should examine moderating or mediating factors between age, acculturation, religiosity, and heavy drinking that might be targets for behavioral interventions.
Objective: To estimate the prevalence and identify correlates of depressive symptoms among immigr... more Objective: To estimate the prevalence and identify correlates of depressive symptoms among immigrant Latino sexual minorities. Methods: Respondent-driven sampling (RDS) was used to estimate the prevalence of depressive symptoms, and univariate and multivariable analyses were conducted to identify correlates of depressive symptoms. Results: Unweighted and RDS-weighted prevalence estimates of depressive symptoms were 69.2% and 74.8%, respectively. In the multivariable analysis, low social support, sexual compulsivity, and high self-esteem were significantly associated with increased depressive symptoms. Conclusions: A need exists for culturally congruent mental health services for immigrant Latino sexual minorities in the southern United States.
Nicotine & tobacco research : official journal of the Society for Research on Nicotine and Tobacco, 2014
E-cigarettes are relatively new products that simulate the smoking experience. This descriptive s... more E-cigarettes are relatively new products that simulate the smoking experience. This descriptive study assessed changes in e-cigarette availability and promotions among retailers in 11 college communities in North Carolina and Virginia during a 1-year period. During the spring of 2012 and 2013, observers completed assessments in 320 tobacco-selling retailers, including grocery and convenience stores, pharmacies, and tobacco shops. Assessors collected e-cigarette availability, advertising, price, and promotions. E-cigarette availability increased among retailers from 24.7% in 2012 to 59.9% in 2013. They were available in the form of disposables and reusable kits and were most frequently available in tobacco shops, convenience stores, and pharmacies. The average price for disposables was $9.70 (SD = 1.07) in 2012 and $9.61 (SD = 2.10) in 2013; the average price for kits was $39.58 (SD = 15.79) in 2012 and $32.59 (SD = 18.65) in 2013. The presence of interior advertising increased from ...
College youth susceptible to waterpipe tobacco smoking (WTS) represent an important target to int... more College youth susceptible to waterpipe tobacco smoking (WTS) represent an important target to intervene upon in order to prevent their uptake of this product. This study examined the performance of a 4-item susceptibility measure to WTS to predict future waterpipe use and correlates of susceptibility. A cohort of college students from 11 university campuses in North Carolina and Virginia completed an online survey in 2012 and again in 2013 that assessed WTS susceptibility and subsequent waterpipe use. Tobacco use, marijuana use, binge drinking, and sensation seeking were also assessed. Overall, 964 students who reported having never used waterpipe tobacco in 2012 completed the online surveys both years. Overall, about 27% of college youth were susceptible to WTS each year. Participants susceptible in 2012 were 2.5 times more likely to report having used waterpipe tobacco the subsequent year than non-susceptible participants after controlling for significant correlates of waterpipe use. Correlates of susceptibility were: being male, past 30 day cigarette smoking, use of other tobacco products, binge drinking and marijuana use, as well as higher sensation seeking. A 4-item WTS susceptibility measure predicts future WTS. This measure can be used to identify and intervene upon susceptible college youth to curb further exploration of WTS. Indeed, a nontrivial proportion of college students found susceptible go on to use waterpipe tobacco within a year.
Journal of The American Academy of Child and Adolescent Psychiatry, 1999
ObjectiveTo examine risk for suicide attempts among 180 consecutively referred adolescents during... more ObjectiveTo examine risk for suicide attempts among 180 consecutively referred adolescents during the first 5 years after discharge from an inpatient psychiatry unit.
Journal of The American Academy of Child and Adolescent Psychiatry, 1998
ObjectiveTo compare psychiatric diagnoses of hospitalized adolescents who (a) have made previous ... more ObjectiveTo compare psychiatric diagnoses of hospitalized adolescents who (a) have made previous but no recent suicide attempts, (b) have recently made their first suicide attempt, (c) have recently made a second or subsequent attempt, or (d) have never made an attempt.
PURPOSE: The purpose of the study is to examine variation in adolescent drug-use patterns by usin... more PURPOSE: The purpose of the study is to examine variation in adolescent drug-use patterns by using latent class regression analysis and evaluate the properties of an estimating-equations approach under different cluster-unit trial designs. METHODS: A set of second-order estimating equations for latent class models under the cluster-unit trial design are proposed. This approach models the correlation within subclusters (drug-use behaviors), but ignores the correlation within clusters (communities). A robust covariance estimator is proposed that accounts for within-cluster correlation. Performance of this approach is addressed through a Monte Carlo simulation study, and practical implications are illustrated by using data from the National Evaluation of the Enforcing Underage Drinking Laws Randomized Community Trial. RESULTS: The example shows that the proposed method provides useful information about the heterogeneous nature of drug use by identifying two subtypes of adolescent problem drinkers. A Monte Carlo simulation study supports the proposed estimation method by suggesting that the latent class model parameters were unbiased for 30 or more clusters. Consistent with other studies of generalized estimating equation (GEE) estimators, the robust covariance estimator tended to underestimate the true variance of regression parameters, but the degree of inflation in the test size was relatively small for 70 clusters and only slightly inflated for 30 clusters. CONCLUSIONS: The proposed model for studying adolescent drug use provides an alternative to standard diagnostic criteria, focusing on the nature of the drug-use profile, rather than relying on univariate symptom counts. The second-order GEE-type estimation procedure provided a computationally feasible approach that performed well for a moderate number of clusters and was consistent with prior studies of GEE under the generalized linear model framework. Ann Epidemiol 2006;16:850e859. Ó
This study assessed the relationship between community characteristics and alcohol use among 6,63... more This study assessed the relationship between community characteristics and alcohol use among 6,636 youth, aged from 14 to 20, in 2004. After adjusting for individual-level characteristics, youth from communities with a greater proportion of grandparents as caregivers, larger numbers of married couple families, and higher employment rates were significantly less likely to report past 30-day alcohol use. Youth from communities with higher median household income were significantly more likely to report past 30-day alcohol use. Adolescents in communities with a greater percentage of whites were significantly more likely to report binge drinking. The results indicate that the community context is an important predictor of alcohol use.
The etiologic role of corticosteroid therapy in tendon rupture is controversial. This study compa... more The etiologic role of corticosteroid therapy in tendon rupture is controversial. This study compared the effects of injected versus iontophoretically delivered corticosteroid on the normal rabbit Achilles tendon. Rabbits were divided into three treatment groups: (1) corticosteroid injections, (2) iontophoretically delivered corticosteroid, and (3) no treatment. One tendon of each rabbit in the treatment groups was treated with either drug injection or iontophoresis; the tendon of the other leg served as a control. Some tendons were used for testing elastic modulus, ultimate load, and ultimate stress, while the remaining tendons were evaluated histologically. Injections of either corticosteroid or saline into the tendon sheath resulted in short-term changes in tendon biomechanical characteristics and somewhat higher histologic severity scores; however, iontophoretic delivery of corticosteroid or saline did not affect either significantly. Iontophoresis using sterile water or corticosteroid resulted in minimal or no biochemical and histologic changes in the tendon compared with injection of either substance. The method of corticosteroid delivery may be as important as the actual drug effects on the biomechanical and histologic properties of tendons.
Maximum likelihood estimation is computationally infeasible for latent variable models involving ... more Maximum likelihood estimation is computationally infeasible for latent variable models involving multivariate categorical responses, in particular for the LISCOMP model. A three-stage generalized least squares approach introduced by Muthén (1983, 1984) can experience problems of instability, bias, non-convergence, and non-positive definiteness of weight matrices in situations of low prevalence, small sample size and large numbers of observed indicator variables. We propose a quadratic estimating equations approach that only requires specification of the first two moments. By performing simultaneous estimation of parameters, this method does not encounter the problems mentioned above and experiences gains in efficiency. Methods are compared through a numerical study and an application to a study of life-events and neurotic illness.
Page 1. Psychology and Health, 2000, Vol. 15, pp. 239-254 Reprints available directly from the Pu... more Page 1. Psychology and Health, 2000, Vol. 15, pp. 239-254 Reprints available directly from the Publisher Photocopying permitted by license only 0 2000 OPA (Overseas Publishers Association) NV Published by license under ...
Objective: Diabetic retinopathy (DR) is a major cause of visual impairment and blindness in adult... more Objective: Diabetic retinopathy (DR) is a major cause of visual impairment and blindness in adults. Antioxidant nutrients, such as vitamins C and E and beta-carotene, may be protective of some eye disorders, such as cataract and age-related macular degeneration, but a relationship between these nutrients and DR has yet to be defined. The purpose of this study was to examine the relation between dietary and supplement intakes of vitamins C, E, and beta-carotene and the risk of DR.
In this study, the authors focused on signs of early childhood misbehavior that might be linked t... more In this study, the authors focused on signs of early childhood misbehavior that might be linked to the risk of becoming tobacco-dependent. Standardized teacher ratings of misbehavior were obtained for an epidemiologic sample of first graders entering an urban mid-Atlantic public school system in 1985 and 1986. Fifteen years later, 1,692 of the students were reassessed (nearly 75% of the
In longitudinal behavioural studies, it is common to have multiple categorical indicators for mea... more In longitudinal behavioural studies, it is common to have multiple categorical indicators for measuring a theoretical construct of interest. A latent class model is presented that accounts for the structure in a set of correlated, categorical variables measured at discrete time periods, drawing information from these variables to form a smaller number of latent classes. The dependence of the resulting latent class model parameters on suspected factors over time is simultaneously modelled using a baseline-category logistic regression model. Estimation of the model parameters is achieved using an estimating equations procedure. A motivating example is provided from a longitudinal study of suspected linkages between monitoring or supervision by parents and the occurrence of drug use behaviours in an epidemiologic sample of school-attending youths.
The present study uses latent class methods and multiple regression to shed light on hypothesized... more The present study uses latent class methods and multiple regression to shed light on hypothesized cocaine dependence syndromes experienced by community residents, who initiated cocaine use within 24 months of survey assessment, and explores possible variation in risk. Identified within public use data files from the United States National Household Surveys on Drug Abuse (NHSDA), and with assessments completed between 1995 and 1998, the study sample consists of 927 recent-onset cocaine users, defined as having initiated cocaine use no more than 24 months prior to assessment (approximate median elapsed time since onset of use approximately 12-13 months). The NHSDA included items to assess seven clinical features often associated with cocaine dependence, which were used in latent class modeling. Empirically derived latent classes, in conjunction with prior theory, tend to support a three-class solution, according to which 4% of recent-onset users are members of a class that resembles the DSM-IV cocaine dependence syndrome (mean: 5.4 clinical features (CF)); 16% might be in a cocaine dependence prodrome (mean: 2.4 CF); 80% of recent-onset cocaine users had few or no clinical features (mean<1 CF). Results from latent class regressions indicate that susceptibility to rapid transition from first cocaine use to onset of the LCA-assigned cocaine dependence syndrome might depend upon whether the user starts smoking crack-cocaine and, independently, age at first cocaine use.
Journal of the Royal Statistical Society: Series A (Statistics in Society), 2000
Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder which is most of... more Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder which is most often diagnosed in childhood with symptoms often persisting into adulthood. Elevated rates of substance use disorders have been evidenced among those with ADHD, but recent research focusing on the relationship between subtypes of ADHD and specific drugs is inconsistent. We propose a latent transition model (LTM) to guide our understanding of how drug use progresses, in particular marijuana use, while accounting for the measurement error that is often found in self-reported substance use data. We extend the LTM to include a latent class predictor to represent empirically derived ADHD subtypes that do not rely on meeting specific diagnostic criteria. We begin by fitting two separate latent class analysis (LCA) models by using second-order estimating equations: a longitudinal LCA model to define stages of marijuana use, and a cross-sectional LCA model to define ADHD subtypes. The LTM model parameters describing the probability of transitioning between the LCA-defined stages of marijuana use and the influence of the LCA-defined ADHD subtypes on these transition rates are then estimated by using a set of first-order estimating equations given the LCA parameter estimates. A robust estimate of the LTM parameter variance that accounts for the variation due to the estimation of the two sets of LCA parameters is proposed. Solving three sets of estimating equations enables us to determine the underlying latent class structures independently of the model for the transition rates and simplifying assumptions about the correlation structure at each stage reduces the computational complexity.
An earlier study reported on the development of a scale to measure feeling states during acute bo... more An earlier study reported on the development of a scale to measure feeling states during acute bouts of exercise: the Exercise-induced Feeling Inventory (EFI-A). The present study reports on the psychometric properties of a revised scale to assess responses to habitual or chronic physical activity: the EFI-C. The EFI-C was administered during baseline testing to 830 sedentary men and women patients with a mean age of 51.5 years. Factor analytic procedures revealed that the EFI-C consisted of two factors, one assessing pleasant feeling states and a second that taps the unpleasant experience of physical exhaustion. Both subscales have excellent internal consistency reliability coefficients (~0.90) and are reasonably stable over time, having test-retest coefficients in excess of 0.70. The scales correlated in expected directions with related constructs and in preliminary analyses showed an anticipated pattern of sensitivity to physical activity interventions. Mean scores for various demographic groups are reported. Future research should examine whether the EFI-C is a predictor of adherence to physical activity and its potential role in mediating the positive mental health effects of physical activity.
This study describes diurnal variations in feeling states in 84 women as a function of involvemen... more This study describes diurnal variations in feeling states in 84 women as a function of involvement in physical activity. Women completed feeling state checklists before and after bouts of vigorous physical activity that lasted a minimum of 20 min and on a stratified random-sampling protocol in response to a stimulus from an electronic pager. Participants self-reported the date, the time of day, the stimulus for responding, their current feeling states, and their ongoing activity. A total of 7,295 complete mood and activity reports were recorded in response to pager calls that were further coded into experience samplings that occurred on a nonexercise day, prior to exercise on an exercise day, and following exercise on an exercise day. Multilevel modeling analyses showed that in samplings recorded following exercise on exercise days, positive engagement, revitalization, and tranquility were elevated in comparison with predicted diurnal patterns.
Few studies have examined correlates of heavy drinking among rural immigrant Latino men. This ana... more Few studies have examined correlates of heavy drinking among rural immigrant Latino men. This analysis identified correlates of typical week drunkenness and past 30-day heavy episodic drinking, within a sample of immigrant Latino men in rural North Carolina (n = 258). In the bivariate analyses, Mexican birth, entering the United States as an adult, and year-round employment were associated with increased odds of typical week drunkenness, and higher acculturation and affiliation with a religion with strict prohibitions against drinking alcohol were associated with lower odds of typical week drunkenness. Being older, Mexican birth, entering the United States as an adult, and lower acculturation were associated with increased odds of heavy episodic drinking, and affiliation with a religion with strict prohibitions against drinking alcohol and completing high school were associated with decreased odds of heavy episodic drinking. In multivariable modeling, only religious affiliation was associated with typical week drunkenness. Mexican birth, entering the United States as an adult, and lower acculturation were associated with increased odds of heavy episodic drinking, and affiliation with a religion with strict prohibitions against drinking alcohol and completing high school were associated with lower odds of heavy episodic drinking. The health of minority men in the United States has been neglected, and immigrant Latino men comprise a particularly vulnerable population. This analysis provides initial data on some factors associated with heavy drinking within a population about which little is known. Future studies should examine moderating or mediating factors between age, acculturation, religiosity, and heavy drinking that might be targets for behavioral interventions.
Objective: To estimate the prevalence and identify correlates of depressive symptoms among immigr... more Objective: To estimate the prevalence and identify correlates of depressive symptoms among immigrant Latino sexual minorities. Methods: Respondent-driven sampling (RDS) was used to estimate the prevalence of depressive symptoms, and univariate and multivariable analyses were conducted to identify correlates of depressive symptoms. Results: Unweighted and RDS-weighted prevalence estimates of depressive symptoms were 69.2% and 74.8%, respectively. In the multivariable analysis, low social support, sexual compulsivity, and high self-esteem were significantly associated with increased depressive symptoms. Conclusions: A need exists for culturally congruent mental health services for immigrant Latino sexual minorities in the southern United States.
Nicotine & tobacco research : official journal of the Society for Research on Nicotine and Tobacco, 2014
E-cigarettes are relatively new products that simulate the smoking experience. This descriptive s... more E-cigarettes are relatively new products that simulate the smoking experience. This descriptive study assessed changes in e-cigarette availability and promotions among retailers in 11 college communities in North Carolina and Virginia during a 1-year period. During the spring of 2012 and 2013, observers completed assessments in 320 tobacco-selling retailers, including grocery and convenience stores, pharmacies, and tobacco shops. Assessors collected e-cigarette availability, advertising, price, and promotions. E-cigarette availability increased among retailers from 24.7% in 2012 to 59.9% in 2013. They were available in the form of disposables and reusable kits and were most frequently available in tobacco shops, convenience stores, and pharmacies. The average price for disposables was $9.70 (SD = 1.07) in 2012 and $9.61 (SD = 2.10) in 2013; the average price for kits was $39.58 (SD = 15.79) in 2012 and $32.59 (SD = 18.65) in 2013. The presence of interior advertising increased from ...
College youth susceptible to waterpipe tobacco smoking (WTS) represent an important target to int... more College youth susceptible to waterpipe tobacco smoking (WTS) represent an important target to intervene upon in order to prevent their uptake of this product. This study examined the performance of a 4-item susceptibility measure to WTS to predict future waterpipe use and correlates of susceptibility. A cohort of college students from 11 university campuses in North Carolina and Virginia completed an online survey in 2012 and again in 2013 that assessed WTS susceptibility and subsequent waterpipe use. Tobacco use, marijuana use, binge drinking, and sensation seeking were also assessed. Overall, 964 students who reported having never used waterpipe tobacco in 2012 completed the online surveys both years. Overall, about 27% of college youth were susceptible to WTS each year. Participants susceptible in 2012 were 2.5 times more likely to report having used waterpipe tobacco the subsequent year than non-susceptible participants after controlling for significant correlates of waterpipe use. Correlates of susceptibility were: being male, past 30 day cigarette smoking, use of other tobacco products, binge drinking and marijuana use, as well as higher sensation seeking. A 4-item WTS susceptibility measure predicts future WTS. This measure can be used to identify and intervene upon susceptible college youth to curb further exploration of WTS. Indeed, a nontrivial proportion of college students found susceptible go on to use waterpipe tobacco within a year.
Journal of The American Academy of Child and Adolescent Psychiatry, 1999
ObjectiveTo examine risk for suicide attempts among 180 consecutively referred adolescents during... more ObjectiveTo examine risk for suicide attempts among 180 consecutively referred adolescents during the first 5 years after discharge from an inpatient psychiatry unit.
Journal of The American Academy of Child and Adolescent Psychiatry, 1998
ObjectiveTo compare psychiatric diagnoses of hospitalized adolescents who (a) have made previous ... more ObjectiveTo compare psychiatric diagnoses of hospitalized adolescents who (a) have made previous but no recent suicide attempts, (b) have recently made their first suicide attempt, (c) have recently made a second or subsequent attempt, or (d) have never made an attempt.
PURPOSE: The purpose of the study is to examine variation in adolescent drug-use patterns by usin... more PURPOSE: The purpose of the study is to examine variation in adolescent drug-use patterns by using latent class regression analysis and evaluate the properties of an estimating-equations approach under different cluster-unit trial designs. METHODS: A set of second-order estimating equations for latent class models under the cluster-unit trial design are proposed. This approach models the correlation within subclusters (drug-use behaviors), but ignores the correlation within clusters (communities). A robust covariance estimator is proposed that accounts for within-cluster correlation. Performance of this approach is addressed through a Monte Carlo simulation study, and practical implications are illustrated by using data from the National Evaluation of the Enforcing Underage Drinking Laws Randomized Community Trial. RESULTS: The example shows that the proposed method provides useful information about the heterogeneous nature of drug use by identifying two subtypes of adolescent problem drinkers. A Monte Carlo simulation study supports the proposed estimation method by suggesting that the latent class model parameters were unbiased for 30 or more clusters. Consistent with other studies of generalized estimating equation (GEE) estimators, the robust covariance estimator tended to underestimate the true variance of regression parameters, but the degree of inflation in the test size was relatively small for 70 clusters and only slightly inflated for 30 clusters. CONCLUSIONS: The proposed model for studying adolescent drug use provides an alternative to standard diagnostic criteria, focusing on the nature of the drug-use profile, rather than relying on univariate symptom counts. The second-order GEE-type estimation procedure provided a computationally feasible approach that performed well for a moderate number of clusters and was consistent with prior studies of GEE under the generalized linear model framework. Ann Epidemiol 2006;16:850e859. Ó
This study assessed the relationship between community characteristics and alcohol use among 6,63... more This study assessed the relationship between community characteristics and alcohol use among 6,636 youth, aged from 14 to 20, in 2004. After adjusting for individual-level characteristics, youth from communities with a greater proportion of grandparents as caregivers, larger numbers of married couple families, and higher employment rates were significantly less likely to report past 30-day alcohol use. Youth from communities with higher median household income were significantly more likely to report past 30-day alcohol use. Adolescents in communities with a greater percentage of whites were significantly more likely to report binge drinking. The results indicate that the community context is an important predictor of alcohol use.
The etiologic role of corticosteroid therapy in tendon rupture is controversial. This study compa... more The etiologic role of corticosteroid therapy in tendon rupture is controversial. This study compared the effects of injected versus iontophoretically delivered corticosteroid on the normal rabbit Achilles tendon. Rabbits were divided into three treatment groups: (1) corticosteroid injections, (2) iontophoretically delivered corticosteroid, and (3) no treatment. One tendon of each rabbit in the treatment groups was treated with either drug injection or iontophoresis; the tendon of the other leg served as a control. Some tendons were used for testing elastic modulus, ultimate load, and ultimate stress, while the remaining tendons were evaluated histologically. Injections of either corticosteroid or saline into the tendon sheath resulted in short-term changes in tendon biomechanical characteristics and somewhat higher histologic severity scores; however, iontophoretic delivery of corticosteroid or saline did not affect either significantly. Iontophoresis using sterile water or corticosteroid resulted in minimal or no biochemical and histologic changes in the tendon compared with injection of either substance. The method of corticosteroid delivery may be as important as the actual drug effects on the biomechanical and histologic properties of tendons.
Maximum likelihood estimation is computationally infeasible for latent variable models involving ... more Maximum likelihood estimation is computationally infeasible for latent variable models involving multivariate categorical responses, in particular for the LISCOMP model. A three-stage generalized least squares approach introduced by Muthén (1983, 1984) can experience problems of instability, bias, non-convergence, and non-positive definiteness of weight matrices in situations of low prevalence, small sample size and large numbers of observed indicator variables. We propose a quadratic estimating equations approach that only requires specification of the first two moments. By performing simultaneous estimation of parameters, this method does not encounter the problems mentioned above and experiences gains in efficiency. Methods are compared through a numerical study and an application to a study of life-events and neurotic illness.
Page 1. Psychology and Health, 2000, Vol. 15, pp. 239-254 Reprints available directly from the Pu... more Page 1. Psychology and Health, 2000, Vol. 15, pp. 239-254 Reprints available directly from the Publisher Photocopying permitted by license only 0 2000 OPA (Overseas Publishers Association) NV Published by license under ...
Objective: Diabetic retinopathy (DR) is a major cause of visual impairment and blindness in adult... more Objective: Diabetic retinopathy (DR) is a major cause of visual impairment and blindness in adults. Antioxidant nutrients, such as vitamins C and E and beta-carotene, may be protective of some eye disorders, such as cataract and age-related macular degeneration, but a relationship between these nutrients and DR has yet to be defined. The purpose of this study was to examine the relation between dietary and supplement intakes of vitamins C, E, and beta-carotene and the risk of DR.
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Papers by Beth Reboussin