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Objectives@#This study aimed to assess the status of the Journal of the Korean Academy of Child and Adolescent Psychiatry (JKACAP) and propose measures for its growth and development. @*Methods@#The study was conducted using a questionnaire survey targeting members of the Korean Academy of Child and Adolescent Psychiatry. The six key elements analyzed were Access to the journal, Convenience following conversion to English, Recognition as an international journal and institutional achievements, Author perspectives on manuscript submission,Transition to an online-only journal, and Content and identity of the journal. @*Results@#The survey revealed that email notification was highly effective for Journal Accessibility, with the website and search engines also frequently being used by members. Conversion to English in 2018 initially impacted readability and submission rates, but these concerns have decreased over time. However, the Recognition of JKACAP as an international academic journal was still not on par with SCIE journals, highlighting the need for further efforts towards SCIE inclusion. Despite these challenges and limited research opportunities, there was an active intention among members to submit manuscripts. Respondents showed a notable preference for the Transition to an online-only journal. Regarding content and identity of the JKACAP, members predominantly favored review articles and perceived the journal as a research and communication platform for Korean child and adolescent psychiatrists. @*Conclusion@#The results indicate the need for JKACAP to enhance its digital accessibility, provide more support for domestic and international authors, and actively seek SCIE indexing. Addressing the varied content preferences of its members, improving the submission process, and transitioning to an online-only format could further its growth and solidify its position as an internationally recognized academic journal in the field of child and adolescent psychiatry.
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Objectives@#This study examined the changes in anxiety and depressive symptoms in the parents of Korean adults with autism spectrum disorder (ASD) after participating in the Korean version of the Program for the Education and Enrichment of Relational Skills for Young Adults (PEERS ® -YA-K). @*Methods@#Forty-six parents were enrolled (mean age 54.7 years; 22 fathers and 24 mothers), of whom 27 participated in the PEERS ® -YA-K as social coaches. Participants completed self-report scales, including the Test of Young Adult Social Skills Knowledge (TYASSK), Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), and Symptom Check-List-90-R (SCL-90-R). The scales were administered three times: before and after the 16-week program and 4 months after the program ended. Differences between participant variables at pretreatment, post-treatment, and follow-up were analyzed using paired-sample t-tests. @*Results@#Participants showed a significant improvement in their social skills knowledge (TYASSK) (:p<0.01). There was a significant improvement in the BAI and BDI scores of parents with severe depressive and anxiety symptoms at the baseline (p<0.05). Paternal paranoia and maternal hostility results also significantly improved on the SCL-90-R. @*Conclusion@#This study suggests that PEERS ® -YA-K can reduce parental anxiety and depressive symptoms. To the best of our knowledge, this is the first to compare the degree of depression and anxiety after PEERS ® -YA-K in parents of adults with ASD.
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Objectives@#Regression, while not a core symptom of autism spectrum disorder (ASD), has been suggested to be a distinct subtype by previous studies. Therefore, this study aimed to explore the prevalence and clinical differences between those with and without regression in children with ASD. @*Methods@#This study includes data from toddlers and young children aged 2–7 years acquired from other projects at Seoul National University Bundang Hospital. The presence and characteristics of regression were explored using question items #11–28 from the Autism Diagnostic Interview-Revised. Chi-square and independent t-tests were used to compare various clinical measurements such as autistic symptoms, adaptative behavior, intelligence, and perinatal factors. @*Results@#Data from 1438 young children (1020 with ASD) were analyzed. The overall prevalence rate of regression, which was mainly related to language-related skills, was 10.2% in the ASD group, with an onset age of 24 months. Regarding clinical characteristics, patients with ASD and regression experienced ASD symptoms, especially restricted and repetitive interests and behaviors, with greater severity than those without regression. Furthermore, there were significant associations between regression and hypertension/placenta previa. @*Conclusion@#In-depth surveillance and proactive interventions targeted at young children with ASD and regression should focus on autistic symptoms and other areas of functioning.
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no abstract available.
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Objectives@#Restricted and repetitive behaviors (RRBs) are a core symptom in the diagnosis of autism spectrum disorder (ASD). The complexity of behavioral patterns has called for the creation of phenotypically homogeneous subgroups among individuals with ASD.The purpose of this study was 1) to investigate the different types of RRBs and 2) to explore whether subgroups created by RRBs would show unique levels of functioning in toddlers and young children with ASD. @*Methods@#A total of 313 children with ASD, aged 12–42 months were included in the analysis. The Autism Diagnostic Interview-Revised was used to obtain information on the different types of RRBs by grouping 15 items into six categories. The Vineland Adaptive Behaviors Scale, a parent-reported questionnaire, was used to measure adaptive functioning. A portion of the children were analyzed separately for verbal-related RRBs based on their expressive language level. Two-step cluster analysis using RRB groups as features was used to create subgroups. Analysis of covariance while covarying for age and language was performed to explore the clinical characteristics of each cluster group. @*Results@#Sensory-related RRBs were the most prevalent, followed by circumscribed interests, interest in objects, resistance to change, and repetitive body movements. A subset of the children was analyzed separately to explore verbal-related RRBs. Four cluster groups were created based on reported RRBs, with multiple RRBs demonstrating significant delays in adaptive functioning. @*Conclusion@#Heterogeneity of RRBs emerges at a young age. The different patterns of RRBs can be used as valuable information to determine developmental trajectories with better implications for treatment approaches.
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Objective@#This cross-cultural study aims to examine the psychometric properties of the Social Responsiveness Scale (SRS) and to determine the best-estimate-cut-off scores for the diagnosis of autism spectrum disorder (ASD) in Korean preschool children. @*Methods@#A total of 563 children was recruited from multiple sources, including Seoul National University Bundang Hospital. Participants were assessed by a multidisciplinary research team using multiple diagnostic tools based on DSM-5 diagnostic criteria. Discriminative validity was tested by comparing the difference in SRS scores between ASD and non-ASD groups. Convergent validity was tested by examining correlations between SRS scores with other diagnostic instruments. A receiver operation characteristic curve analysis was conducted to test the sensitivity and specificity of SRS and to determine the best-estimate-cut-off scores for screening ASD in Korean preschool children. @*Results@#There were significant differences in the total SRS scores between the ASD (n=242) and non-ASD group (n=321) (p<0.01, 95% confidence interval [CI]: 14.08–17.24). The differences were significant even after adjusting for age. SRS scores were significantly correlated with other prescreening diagnostic tools for ASD. The best-estimate cut-off score to screen ASD was 55 (area under curve=0.88, sensitivity 78.1%, specificity 86.6%). @*Conclusion@#The SRS is a valid and reliable instrument to screen and aid in the diagnosis of ASD in Korean preschool children. The adjusted cut-off scores, notably lower than in the original U.S. version, may yield a more accurate diagnosis by reflecting transcultural differences.
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Objective@#This study aimed to examine the validity of the Korean version of the Autism Diagnostic Interview-Revised (K-ADI-R) and determine its efficacy in identifying individuals with autism spectrum disorder (ASD). @*Methods@#Data were pooled from several past and ongoing studies as well as clinical records acquired at Seoul National University Bundang Hospital from 2008 to 2017. The K-ADI-R were administered and scored by trained research reliable examiners. Measurements to investigate the validity of the K-ADI-R was through sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV), and Cohen’s kappa. @*Results@#A total of 1,271 (age 88.9±62.42 months, male=927) participants were included. The K-ADI-R yielded strong psychometric properties with high sensitivity (86.06–99.27%), specificity (84.75–99.55%), PPV (92.33–99.72%), and NPV (79.43–98.64%). There were significant differences in item scores across the K-ADI-R diagnostic algorithm regardless of age and sex (p<0.001). Agreement between the K-ADI-R and other ASD related measurements ranged between levels of good to excellent. @*Conclusion@#Despite language or cultural boundaries, the K-ADI-R demonstrated high levels of sensitivity, specificity, PPV, and NPV within a wide range of participants; hence, suggesting promising usage as a valuable diagnostic instrument for individuals with ASD.
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Objective@#This study examined how state and trait anxiety of adolescents with autism spectrum disorders (ASD) are associated with their demographic characteristics, repetitive and restricted behaviors (RRBs), and internalizing and externalizing problem behaviors. @*Methods@#A total of 96 participants with ASD (mean age=14.30 years; 91 males) completed a battery of tests including the State/Trait Anxiety Inventory (STAI), the Autism Diagnostic Interview-Revised, the Social Responsiveness Scale (SRS), and a cognitive test measuring intelligence quotient (IQ). Participants’ parents completed the Child Behavior Checklist (CBCL). Pearson’s correlations among age, IQ, two subscales of the STAI (i.e., STAIS and STAIT, measuring self-reported state and trait anxiety, respectively), and the Anxiety subscale of CBCL (i.e., CBCL-Anxiety, measuring parent-reported trait anxiety) were computed. Subsequently, Pearson’s correlations were computed among the three anxiety measures, RRBs, and problem behaviors, while controlling for participants’ age and IQ. @*Results@#The STAIS and CBCL-Anxiety were both significantly correlated with higher age, sensory sensitivity, depressive symptoms, somatic complaints, and aggressive behaviors. All three anxiety variables were significantly and positively correlated with total SRS RRB scores. Additionally, the STAIS and STAIT were significantly associated with more severe Compulsion/Adherence behaviors, and the CBCL-Anxiety was also significantly associated with more severe Rule-breaking Behaviors. @*Conclusion@#Self-reported state anxiety showed association patterns similar to those of parent-reported trait anxiety. Future studies investigating the precise operationalization of different anxiety instruments are needed to accurately measure the anxiety of adolescents with ASD.
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Objective@#Adults with autism spectrum disorders (ASD) experience significant difficulties with executive functioning (EF) and related adaptive skills, yet the lack of interventions in South Korea targeting these areas has resulted in a heightened need to develop an evidence- based program. Therefore, we developed a novel intervention aiming to enhance everyday EF and daily adaptive skills in adults with high-functioning ASD and conducted a pilot study to evaluate the validity and feasibility of the program. @*Methods@#A behavioral intervention of 10-weekly sessions was developed based on literature searches and focus group interviews. Seven adults with high-functioning ASD (mean age=20.29) participated in a single-group pilot trial. We used self and parent-report questionnaires as well as skills measured by assessment instruments to analyze differences before and after the intervention. @*Results@#Significant improvements were shown in everyday EF, including time management, organization, self-restraint, and regulation of emotions. Additionally, results demonstrated an enhancement in adaptive functioning, especially in the subdomains of daily living skills. Analyses of parental outcomes only revealed a significant decrease in the scores of emotion regulation. @*Conclusion@#The current study provides good evidence for the validity and feasibility of an intervention to improve everyday EF and adaptive skills in adults with ASD.
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Objectives@#This study identified the association between excessive exposure to screen media and behavioral and emotional problems in elementary school students. @*Methods@#A total of 331 parents of children aged 7–10 years were recruited from “The Kids Cohort for Understanding of Internet Addiction Risk Factors in Early Childhood (K-CURE)” study. Children’s demographics, household media ownership, screen time, and behavioral/emotional problems were assessed using a parental questionnaire. Children’s behavior/emotional problems were measured using the Korean version the of Child Behavior Checklist (K-CBCL) score. @*Results@#The total K-CBCL score in the screen overuse group was 51.18±9.55, significantly higher than 47.28±10.09 in the control group (t=2.14, p=0.05). For each subscale, the externalization score (51.65±10.14, 48.33±8.97, respectively; t=2.02, p<0.05), social problem score (55.41±6.11, 53.24±5.19, respectively; t=2.27, p<0.05), and rule breaking behavior score (55.71±6.11, 53.24±5.19, respectively; t=2.27, p<0.05) were significantly higher in the screen overuse group than in the control group. In addition, the screen overuse group also had a significantly higher usage rate than the control group, even if limited to smartphones, not only on weekdays (3.56±2.08, 1.87±2.02, respectively; t=-4.597, p<0.001) but also weekends (1.62±0.74, 1.19±0.83, respectively; t=-3.14, p=0.003). @*Conclusion@#The study suggested that screen media overuse patterns in children in Korea are particularly relevant to the excessive use of smartphones and are related to higher risks of emotional and behavioral problems.
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Objective@#This cross-cultural study aims to examine the psychometric properties of the Social Responsiveness Scale (SRS) and to determine the best-estimate-cut-off scores for the diagnosis of autism spectrum disorder (ASD) in Korean preschool children. @*Methods@#A total of 563 children was recruited from multiple sources, including Seoul National University Bundang Hospital. Participants were assessed by a multidisciplinary research team using multiple diagnostic tools based on DSM-5 diagnostic criteria. Discriminative validity was tested by comparing the difference in SRS scores between ASD and non-ASD groups. Convergent validity was tested by examining correlations between SRS scores with other diagnostic instruments. A receiver operation characteristic curve analysis was conducted to test the sensitivity and specificity of SRS and to determine the best-estimate-cut-off scores for screening ASD in Korean preschool children. @*Results@#There were significant differences in the total SRS scores between the ASD (n=242) and non-ASD group (n=321) (p<0.01, 95% confidence interval [CI]: 14.08–17.24). The differences were significant even after adjusting for age. SRS scores were significantly correlated with other prescreening diagnostic tools for ASD. The best-estimate cut-off score to screen ASD was 55 (area under curve=0.88, sensitivity 78.1%, specificity 86.6%). @*Conclusion@#The SRS is a valid and reliable instrument to screen and aid in the diagnosis of ASD in Korean preschool children. The adjusted cut-off scores, notably lower than in the original U.S. version, may yield a more accurate diagnosis by reflecting transcultural differences.
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Objective@#This study aimed to examine the validity of the Korean version of the Autism Diagnostic Interview-Revised (K-ADI-R) and determine its efficacy in identifying individuals with autism spectrum disorder (ASD). @*Methods@#Data were pooled from several past and ongoing studies as well as clinical records acquired at Seoul National University Bundang Hospital from 2008 to 2017. The K-ADI-R were administered and scored by trained research reliable examiners. Measurements to investigate the validity of the K-ADI-R was through sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV), and Cohen’s kappa. @*Results@#A total of 1,271 (age 88.9±62.42 months, male=927) participants were included. The K-ADI-R yielded strong psychometric properties with high sensitivity (86.06–99.27%), specificity (84.75–99.55%), PPV (92.33–99.72%), and NPV (79.43–98.64%). There were significant differences in item scores across the K-ADI-R diagnostic algorithm regardless of age and sex (p<0.001). Agreement between the K-ADI-R and other ASD related measurements ranged between levels of good to excellent. @*Conclusion@#Despite language or cultural boundaries, the K-ADI-R demonstrated high levels of sensitivity, specificity, PPV, and NPV within a wide range of participants; hence, suggesting promising usage as a valuable diagnostic instrument for individuals with ASD.
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Objective@#This study examined how state and trait anxiety of adolescents with autism spectrum disorders (ASD) are associated with their demographic characteristics, repetitive and restricted behaviors (RRBs), and internalizing and externalizing problem behaviors. @*Methods@#A total of 96 participants with ASD (mean age=14.30 years; 91 males) completed a battery of tests including the State/Trait Anxiety Inventory (STAI), the Autism Diagnostic Interview-Revised, the Social Responsiveness Scale (SRS), and a cognitive test measuring intelligence quotient (IQ). Participants’ parents completed the Child Behavior Checklist (CBCL). Pearson’s correlations among age, IQ, two subscales of the STAI (i.e., STAIS and STAIT, measuring self-reported state and trait anxiety, respectively), and the Anxiety subscale of CBCL (i.e., CBCL-Anxiety, measuring parent-reported trait anxiety) were computed. Subsequently, Pearson’s correlations were computed among the three anxiety measures, RRBs, and problem behaviors, while controlling for participants’ age and IQ. @*Results@#The STAIS and CBCL-Anxiety were both significantly correlated with higher age, sensory sensitivity, depressive symptoms, somatic complaints, and aggressive behaviors. All three anxiety variables were significantly and positively correlated with total SRS RRB scores. Additionally, the STAIS and STAIT were significantly associated with more severe Compulsion/Adherence behaviors, and the CBCL-Anxiety was also significantly associated with more severe Rule-breaking Behaviors. @*Conclusion@#Self-reported state anxiety showed association patterns similar to those of parent-reported trait anxiety. Future studies investigating the precise operationalization of different anxiety instruments are needed to accurately measure the anxiety of adolescents with ASD.
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Objective@#Adults with autism spectrum disorders (ASD) experience significant difficulties with executive functioning (EF) and related adaptive skills, yet the lack of interventions in South Korea targeting these areas has resulted in a heightened need to develop an evidence- based program. Therefore, we developed a novel intervention aiming to enhance everyday EF and daily adaptive skills in adults with high-functioning ASD and conducted a pilot study to evaluate the validity and feasibility of the program. @*Methods@#A behavioral intervention of 10-weekly sessions was developed based on literature searches and focus group interviews. Seven adults with high-functioning ASD (mean age=20.29) participated in a single-group pilot trial. We used self and parent-report questionnaires as well as skills measured by assessment instruments to analyze differences before and after the intervention. @*Results@#Significant improvements were shown in everyday EF, including time management, organization, self-restraint, and regulation of emotions. Additionally, results demonstrated an enhancement in adaptive functioning, especially in the subdomains of daily living skills. Analyses of parental outcomes only revealed a significant decrease in the scores of emotion regulation. @*Conclusion@#The current study provides good evidence for the validity and feasibility of an intervention to improve everyday EF and adaptive skills in adults with ASD.
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Objectives@#This study identified the association between excessive exposure to screen media and behavioral and emotional problems in elementary school students. @*Methods@#A total of 331 parents of children aged 7–10 years were recruited from “The Kids Cohort for Understanding of Internet Addiction Risk Factors in Early Childhood (K-CURE)” study. Children’s demographics, household media ownership, screen time, and behavioral/emotional problems were assessed using a parental questionnaire. Children’s behavior/emotional problems were measured using the Korean version the of Child Behavior Checklist (K-CBCL) score. @*Results@#The total K-CBCL score in the screen overuse group was 51.18±9.55, significantly higher than 47.28±10.09 in the control group (t=2.14, p=0.05). For each subscale, the externalization score (51.65±10.14, 48.33±8.97, respectively; t=2.02, p<0.05), social problem score (55.41±6.11, 53.24±5.19, respectively; t=2.27, p<0.05), and rule breaking behavior score (55.71±6.11, 53.24±5.19, respectively; t=2.27, p<0.05) were significantly higher in the screen overuse group than in the control group. In addition, the screen overuse group also had a significantly higher usage rate than the control group, even if limited to smartphones, not only on weekdays (3.56±2.08, 1.87±2.02, respectively; t=-4.597, p<0.001) but also weekends (1.62±0.74, 1.19±0.83, respectively; t=-3.14, p=0.003). @*Conclusion@#The study suggested that screen media overuse patterns in children in Korea are particularly relevant to the excessive use of smartphones and are related to higher risks of emotional and behavioral problems.
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Objectives@#The Journal of the Korean Academy of Child and Adolescent Psychiatry (JKACAP) has had a 31 year-long history, sharing research and reviews of children and adolescents’ mental health to promote voluntary participation and communication of the members of this society. Here, we have reviewed the detailed history of the journal from the perspective of developmental progression of JKACAP and discussed the direction of further development. @*Methods@#& Results: We reviewed the journey of the journal by focusing on the effort it took to take the journal to a global standard, and discussed the future direction of progress of JKACAP, based on the opinions raised at the Editor-in-Chiefs’ reunion. @*Conclusion@#JKACAP has just stepped on the path to globalization by being indexed in Emerging Sources Citation Index, PubMed Central, and Scopus. It is time to progress to another dimension, by acknowledging and overcoming more complicated issues, such as augmenting impact of the journal, expanding domains of interdisciplinary collaboration, and more global cooperation.
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Objective@#The primary objective of this study was to predict subgroups of autism spectrum disorder (ASD) based on the Diagnostic Statistical Manual for Mental Disorders-IV Text Revision (DSM-IV-TR) by machine learning (ML). The secondary objective was to set up a ranking of Autism Diagnostic Interview-Revised (ADI-R) diagnostic algorithm items based on ML, and to confirm whether ML can sufficiently predict the diagnosis with these minimum items. @*Methods@#In the first experiment, a multiclass decision forest algorithm was applied, and the diagnostic algorithm score value of 1,269 Korean ADI-R test data was used for prediction. In the second experiment, we used 539 Korean ADI-R case data (over 48 months with verbal language) to apply mutual information to rank items used in the ADI diagnostic algorithm. @*Results@#In the first experiment, the results of predicting in the case of pervasive developmental disorder not otherwise specified as “ASD” were almost three times higher than predicting it as “No diagnosis.” In the second experiment, the top 10 ranking items of ADI-R were mainly related to the quality abnormality of communication. @*Conclusion@#In conclusion, we verified the applicability of ML in diagnosis and found that the application of artificial intelligence for rapid diagnosis or screening of ASD patients may be useful.
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Objective@#The purpose of this study was to examine the visuospatial processing abilities of children with autism spectrum disorder (ASD) using the Rey Osterrieth Complex Figure (ROCF). @*Methods@#One-hundred thirty-four children with ASD [mean age (MA)=113.56 months], 150 siblings of children with ASD (MA= 111.67 months), and 55 typically developing (TD) children (MA=109.02 months) were included in this study. During their one-time visit, participants completed the ROCF, various autism diagnostic assessments, and the Korean-Leiter International Performance ScaleRevised. Repeated-measures Analysis of Covariance (ANCOVA) and post-hoc Tukey-Kramer comparisons were computed to compare the ROCF scores. Partial correlations and multiple regressions were computed to examine the association between ROCF scores and the severity of autistic symptoms, as measured by the Autism Diagnostic Interview-Revised (ADI-R) among children with ASD. @*Results@#There were significant main effects of the analysis group in Structural and Incidental Accuracy, Error, and Style. More siblings than TD children drew in a part-oriented way, but the performance of the sibling group was comparable or superior to that of the TD group in all parameters. Social Interaction scores of children with ASD were significantly associated with Organization scores in Copy condition. Whether or not a child drew in the Part-Oriented style significantly predicted his/her repetitive and restricted behavior scores. @*Conclusion@#The findings add to the evidence for altered visuospatial processing patterns of ASD as a potential inherent and genetic trait and suggest that this particular cognitive style should not be considered as a deficit. Educational and theoretical implications are discussed.
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Objective@#This study tested the validity and reliability of the Behavior Development Screening for Toddlers-Questionnaire-Parents (BeDevel-Q/P), a new autism spectrum disorder (ASD) screening instrument being developed in South Korea. The parents of 24–35-month-old infants were recruited to complete the questionnaire. @*Methods@#The participants were 791 infants aged 24–35 months. There were 623 typically developing infants, 88 infants with ASD, and 80 developmentally delayed infants. For test-retest, the participants were surveyed every 1–4 weeks. Participants were recruited nationwide. Subjects’ parents completed the BeDevel-Q/P and concurrent validity questionnaires. The data were used for statistical analysis. @*Results@#A total of 24 items consisting of 16 items from factor 1 (F1), 6 items from factor 2 (F2), and 2 items from factor 3 (F3), were selected for the final BeDevel-Q/P items. @*Conclusion@#The factors of the screening instrument developed in this study were analyzed, and three factors were extracted, confirming the theoretical foundation of the BeDevel-Q for the parents of 24–35-month-old infants.
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Mitochondrial dysfunction is considered one of the pathophysiological mechanisms of autism spectrum disorder (ASD). However, previous studies of biomarkers associated with mitochondrial dysfunction in ASD have revealed inconsistent results. The objective of this study was to evaluate biochemical markers associated with mitochondrial dysfunction in subjects with ASD and their unaffected family members. Lactate and pyruvate levels, as well as the lactate-to-pyruvate ratio, were examined in the peripheral blood of probands with ASD (Affected Group, AG) and their unaffected family members (biological parents and unaffected siblings, Unaffected Group, UG). Lactate ≥22 mg/dl, pyruvate ≥1.4 mg/dl, and lactate-topyruvate ratio >25 were defined as abnormal. The clinical variables were compared between subjects with higher (>25) and lower (≤25) lactate-topyruvate ratios within the AG. The AG (n=59) had a significantly higher lactate and lactate-to-pyruvate ratio than the UG (n=136). The frequency of subjects with abnormally high lactate levels and lactate-to-pyruvate ratio was significantly higher in the AG (lactate 31.0% vs. 9.5%, ratio 25.9% vs. 7.3%, p<0.01). The relationship between lactate level and the repetitive behavior domain of the Autism Diagnostic Interview-Revised was statistically significant. These results suggest that biochemical markers related to mitochondrial dysfunction, especially higher lactate levels and lactateto-pyruvate ratio, might be associated with the pathophysiology of ASD. Further larger studies using unrelated individuals are needed to control for the possible effects of age and sex on chemical biomarker levels.