The effect of conduct disorder (CD) as a major risk factor of substance use disorder (SUD), contr... more The effect of conduct disorder (CD) as a major risk factor of substance use disorder (SUD), controlling for other psychiatric problems, has been well established in the literature. However, other psychiatric problems are associated as confounders with an increased risk of SUD. When confounding exists, the use of the standard survival analysis approach would lead to a biased estimate of the effect of a time-varying exposure on the time to event. The authors used a G-estimation approach to estimate the causal effect of CD while controlling for time-varying confounders. The present study (N = 1420) found a substantial difference in the estimated hazard ratio of CD (4.49 vs. 1.93) when the results from G-estimation and Cox regression were compared. G-estimation fixed the problem of underestimating the hazard ratio of conduct disorder (CD) while controlling for all measured covariates.
The Conners' Continuous Performance Test (CPT) is a neuropsychological task that has repeatedly b... more The Conners' Continuous Performance Test (CPT) is a neuropsychological task that has repeatedly been shown to differentiate ADHD from normal groups. Several variables may be derived from the Conners' CPT including errors of omission and commission, mean hit reaction time(RT), mean hit RT standard error, d', and β. What each CPT parameter actually assesses has largely been based upon clinical assumptions and the face validity of each measure (e.g., omission errors measure inattention, commission errors measure impulsivity). This study attempts to examine relations between various CPT variables and phenotypic behaviors so as to better understand the various CPT variables. An epidemiological sample of 817 children was administered the Conners' CPT. Diagnostic interviews were conducted with parents to determine ADHD symptom profiles for all children. Children diagnosed with ADHD had more variable RTs, made more errors of commission and omission, and demonstrated poorer perceptual sensitivity than nondiagnosed children. Regarding specific symptoms, generalized estimating equations (GEE) and ANCOVAs were conducted to determine specific relationships between the 18 DSM-IV ADHD symptoms and 6 CPT parameters. CPT performance measures demonstrated significant relationships to ADHD symptoms but did not demonstrate symptom domain specificity according to a priori assumptions. Overall performance on the two signal detection measures, d' and β, was highly related to all ADHD symptoms across symptom domains. Further, increased variability in RTs over time was related to most ADHD symptoms. Finally, it appears that at least 1 CPT variable, mean hit RT, is minimally related to ADHD symptoms as a whole, but does demonstrate some specificity in its link with symptoms of hyperactivity.
In this paper, we examine the effects of age at first substance use, and history of psychiatric d... more In this paper, we examine the effects of age at first substance use, and history of psychiatric disorders, on the development of substance use disorder (SUD) by age 16. We use a prospective, longitudinal design to disaggregate the effects of age at first use and time since first use on the development of adolescent SUD. Second, we test the hypothesis that adolescent SUD is an unlikely progression from early substance use unless children also show other early conduct problems. A population sample of 1420 children from the Great Smoky Mountains Study (GSMS) was assessed annually between ages 9 and 16. Logistic regression models were applied within the hierarchical Bayesian framework, where the covariate effects were described by time-varying parameters having a first-order auto-regressive prior distribution. Posterior analyses based on a Gibbs sampling approach revealed that, controlling for years of exposure, the risk of transition to SUD increased with age at onset for onsets before age 13, but began to fall for onset at 14. Among users, use alone, without early conduct problems, led to a 11% prevalence of SUD by age 16. Past conduct disorder (CD) had a strong additive effect at ages 13–15, but at age 16, when substance use and abuse became more normative, the excess risk from prior CD decreased. Boys, but not girls, with a history of depression were at increased risk of SUD. Anxiety increased the risk of SUD in girls at age 16, but not before that. Results only partially support the study hypothesis; early use was a major predictor of adolescent SUD even in the absence of CD.
This paper examines the relationships between insurance coverage, need, and mental health service... more This paper examines the relationships between insurance coverage, need, and mental health services in a community-based sample of 1,015 youths who were 9, 11, and 13 years old at the beginning of the study. They were followed over a two-year period. A strong measure of need based on a standardized diagnostic interview was available and repeated over three annual waves. Data on service use was collected quarterly across two years. Major findings included: (a) high need (serious emotional disturbance [SED]) was strongly related to use of any mental health services; (b) services use was much more likely to occur with public (Medicaid) insurance coverage than either private or no insurance; (c) considerable unmet need was observed even for youths with SED; (d) school-based mental health services potentially substituted for professional mental health services; and (e) there was little unnecessary use of mental health services in the low need group. The major policy implication of these findings is that the regulation of insurance benefits should be based on level of need, rather than on arbitrary limits which are likely to either reduce the probability of or appropriate amount of care for youths who most need mental health services.
Several “genetic” item-response theory (IRT) models are fitted to the responses of 1086 adolescen... more Several “genetic” item-response theory (IRT) models are fitted to the responses of 1086 adolescent female twins to the 33 multi-category item Mood and Feeling Questionnaire relating to depressive symptomatology in adolescence. A Markov-chain Monte Carlo (MCMC) algorithm is used within a Bayesian framework for inference using Gibbs sampling, implemented in the program WinBUGS 1.4. The final model incorporated separate genetic and non-shared environmental traits (“A and E”) and item-specific genetic effects. Simpler models gave markedly poorer fit to the observations judged by the deviance information criterion (DIC). The common genetic factor showed major loadings on melancholic items, while the environmental factor loaded most highly on items relating to self-deprecation. The MCMC approach provides a convenient and flexible alternative to Maximum Likelihood for estimating the parameters of IRT models for relatively large numbers of items in a genetic context. Additional benefits of the IRT approach are discussed including the estimation of latent trait scores, including genetic factor scores, and their sampling errors.
The linear structural model has provided the statistical backbone of the analysis of twin and fam... more The linear structural model has provided the statistical backbone of the analysis of twin and family data for 25 years. A new generation of questions cannot easily be forced into the framework of current approaches to modeling and data analysis because they involve nonlinear processes. Maximizing the likelihood with respect to parameters of such nonlinear models is often cumbersome and does not yield easily to current numerical methods. The application of Markov Chain Monte Carlo (MCMC) methods to modeling the nonlinear effects of genes and environment in MZ and DZ twins is outlined. Nonlinear developmental change and genotype × environment interaction in the presence of genotype-environment correlation are explored in simulated twin data. The MCMC method recovers the simulated parameters and provides estimates of error and latent (missing) trait values. Possible limitations of MCMC methods are discussed. Further studies are necessary explore the value of an approach that could extend the horizons of research in developmental genetic epidemiology.
The effect of conduct disorder (CD) as a major risk factor of substance use disorder (SUD), contr... more The effect of conduct disorder (CD) as a major risk factor of substance use disorder (SUD), controlling for other psychiatric problems, has been well established in the literature. However, other psychiatric problems are associated as confounders with an increased risk of SUD. When confounding exists, the use of the standard survival analysis approach would lead to a biased estimate of the effect of a time-varying exposure on the time to event. The authors used a G-estimation approach to estimate the causal effect of CD while controlling for time-varying confounders. The present study (N = 1420) found a substantial difference in the estimated hazard ratio of CD (4.49 vs. 1.93) when the results from G-estimation and Cox regression were compared. G-estimation fixed the problem of underestimating the hazard ratio of conduct disorder (CD) while controlling for all measured covariates.
The Conners' Continuous Performance Test (CPT) is a neuropsychological task that has repeatedly b... more The Conners' Continuous Performance Test (CPT) is a neuropsychological task that has repeatedly been shown to differentiate ADHD from normal groups. Several variables may be derived from the Conners' CPT including errors of omission and commission, mean hit reaction time(RT), mean hit RT standard error, d', and β. What each CPT parameter actually assesses has largely been based upon clinical assumptions and the face validity of each measure (e.g., omission errors measure inattention, commission errors measure impulsivity). This study attempts to examine relations between various CPT variables and phenotypic behaviors so as to better understand the various CPT variables. An epidemiological sample of 817 children was administered the Conners' CPT. Diagnostic interviews were conducted with parents to determine ADHD symptom profiles for all children. Children diagnosed with ADHD had more variable RTs, made more errors of commission and omission, and demonstrated poorer perceptual sensitivity than nondiagnosed children. Regarding specific symptoms, generalized estimating equations (GEE) and ANCOVAs were conducted to determine specific relationships between the 18 DSM-IV ADHD symptoms and 6 CPT parameters. CPT performance measures demonstrated significant relationships to ADHD symptoms but did not demonstrate symptom domain specificity according to a priori assumptions. Overall performance on the two signal detection measures, d' and β, was highly related to all ADHD symptoms across symptom domains. Further, increased variability in RTs over time was related to most ADHD symptoms. Finally, it appears that at least 1 CPT variable, mean hit RT, is minimally related to ADHD symptoms as a whole, but does demonstrate some specificity in its link with symptoms of hyperactivity.
In this paper, we examine the effects of age at first substance use, and history of psychiatric d... more In this paper, we examine the effects of age at first substance use, and history of psychiatric disorders, on the development of substance use disorder (SUD) by age 16. We use a prospective, longitudinal design to disaggregate the effects of age at first use and time since first use on the development of adolescent SUD. Second, we test the hypothesis that adolescent SUD is an unlikely progression from early substance use unless children also show other early conduct problems. A population sample of 1420 children from the Great Smoky Mountains Study (GSMS) was assessed annually between ages 9 and 16. Logistic regression models were applied within the hierarchical Bayesian framework, where the covariate effects were described by time-varying parameters having a first-order auto-regressive prior distribution. Posterior analyses based on a Gibbs sampling approach revealed that, controlling for years of exposure, the risk of transition to SUD increased with age at onset for onsets before age 13, but began to fall for onset at 14. Among users, use alone, without early conduct problems, led to a 11% prevalence of SUD by age 16. Past conduct disorder (CD) had a strong additive effect at ages 13–15, but at age 16, when substance use and abuse became more normative, the excess risk from prior CD decreased. Boys, but not girls, with a history of depression were at increased risk of SUD. Anxiety increased the risk of SUD in girls at age 16, but not before that. Results only partially support the study hypothesis; early use was a major predictor of adolescent SUD even in the absence of CD.
This paper examines the relationships between insurance coverage, need, and mental health service... more This paper examines the relationships between insurance coverage, need, and mental health services in a community-based sample of 1,015 youths who were 9, 11, and 13 years old at the beginning of the study. They were followed over a two-year period. A strong measure of need based on a standardized diagnostic interview was available and repeated over three annual waves. Data on service use was collected quarterly across two years. Major findings included: (a) high need (serious emotional disturbance [SED]) was strongly related to use of any mental health services; (b) services use was much more likely to occur with public (Medicaid) insurance coverage than either private or no insurance; (c) considerable unmet need was observed even for youths with SED; (d) school-based mental health services potentially substituted for professional mental health services; and (e) there was little unnecessary use of mental health services in the low need group. The major policy implication of these findings is that the regulation of insurance benefits should be based on level of need, rather than on arbitrary limits which are likely to either reduce the probability of or appropriate amount of care for youths who most need mental health services.
Several “genetic” item-response theory (IRT) models are fitted to the responses of 1086 adolescen... more Several “genetic” item-response theory (IRT) models are fitted to the responses of 1086 adolescent female twins to the 33 multi-category item Mood and Feeling Questionnaire relating to depressive symptomatology in adolescence. A Markov-chain Monte Carlo (MCMC) algorithm is used within a Bayesian framework for inference using Gibbs sampling, implemented in the program WinBUGS 1.4. The final model incorporated separate genetic and non-shared environmental traits (“A and E”) and item-specific genetic effects. Simpler models gave markedly poorer fit to the observations judged by the deviance information criterion (DIC). The common genetic factor showed major loadings on melancholic items, while the environmental factor loaded most highly on items relating to self-deprecation. The MCMC approach provides a convenient and flexible alternative to Maximum Likelihood for estimating the parameters of IRT models for relatively large numbers of items in a genetic context. Additional benefits of the IRT approach are discussed including the estimation of latent trait scores, including genetic factor scores, and their sampling errors.
The linear structural model has provided the statistical backbone of the analysis of twin and fam... more The linear structural model has provided the statistical backbone of the analysis of twin and family data for 25 years. A new generation of questions cannot easily be forced into the framework of current approaches to modeling and data analysis because they involve nonlinear processes. Maximizing the likelihood with respect to parameters of such nonlinear models is often cumbersome and does not yield easily to current numerical methods. The application of Markov Chain Monte Carlo (MCMC) methods to modeling the nonlinear effects of genes and environment in MZ and DZ twins is outlined. Nonlinear developmental change and genotype × environment interaction in the presence of genotype-environment correlation are explored in simulated twin data. The MCMC method recovers the simulated parameters and provides estimates of error and latent (missing) trait values. Possible limitations of MCMC methods are discussed. Further studies are necessary explore the value of an approach that could extend the horizons of research in developmental genetic epidemiology.
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Papers by Al Erkanli