Korean Child Research Articles

The Effect of Teacher’s Teaching-Efficacy and Classroom Environment on Peer-Play Interaction: Mediation Effect of Teacher-Child Interaction

This study examines the mediation effect of teacher-child interactions in the process of the impact of teacher`s teaching-efficacy on childhood education institutions and classroom environment on peer-play interactions. We used data from 970 children aged between 49 and 55 months and 970 homeroom teachers from the fifth Korean Child Panel (2012) of the Korea Institute of Child Care and Education. The model fitness was excellent after data were statistically analyzed with model of structure to testify the relationship and effect among teaching efficacy, classroom environment, teacher-child interactions, and peer-play interactions. First, the analysis also showed that the teacher`s teaching efficacy did not influence peer-play interactions directly, but gave an indirect effect on the peer-play interactions with the mediation of the teacher-child interactions. Second, the classroom environment directly and indirectly influenced the peer-play interactions with the mediation of the teacher-child interactions. Third, the variable of teacher-child interactions was fully effective as a mediating variable in the process of the teaching efficacy and classroom environment influence on teacher-child interactions. Teaching efficacy and classroom environment influenced the peer-play interactions through the mediation of the teacher-child interactions. The significance of mediation effect of the teacher-child interactions was verified through a bootstrapping method.

Association of current phthalate exposure with neurobehavioral development in a national sample.

Previous studies have indicated that phthalate exposure may influence the development of children, but the current data are limited, and controversy remains regarding the sex-specific and age-specific effects of phthalate exposure. We investigated the sex- and age-specific associations of current phthalate exposure with neurobehavioral development scores in a nationally representative sample of 6-18-year-olds participating in the Korean Environmental Health Survey in Children and Adolescents (KorEHS-C). Neurobehavioral development was assessed using the Korean Child Behavior Checklist (CBCL, N=1723) and the Korean Attention Deficit Hyperactivity Disorder Rating Scale (ARS, N=867). We measured the concentrations of phthalate metabolites in urine samples using high-performance liquid chromatography tandem mass spectrometry. The associations between urine phthalate metabolite concentrations and neurobehavioral development were examined by survey regression analysis for complex sampling and penalized regression splines using a generalized additive model. Survey regression analysis revealed that a higher mono-n-butyl phthalate (MnBP) level was associated with social (β=0.60; 95% confidence interval=0.15-1.05), thought (0.55; 0.08-1.03), and attention (0.68; 0.21-1.14) problems on the CBCL. A significant association was found between the MnBP level and the ARS hyperactivity subscale score (0.42; 0.05-0.58). Higher levels of MnBP (0.87; 0.20-1.54), mono-2-ethyl-5-oxohexyl phthalate (MEOHP, 0.61; 0.11-1.11) and mono-2-ethyl-5-hydroxyhexyl phthalate (MEHHP, 0.51; 0.04-0.97) were associated with an increase in thought problems among the girls. Among the younger children aged 6-11 years, significant positive associations between the MnBP (0.71; 0.09-1.33), MECPP (0.74, 0.14-1.34), MEOHP (0.65; 0.10-1.20), and MEHHP (0.71; 0.21-1.21) levels and social problems and between the MnBP (1.11; 0.37-1.84), MEOHP (0.64; 0.13-1.15), and MEHHP (0.66; 0.18-1.14) levels and attention problems were observed. The penalized regression splines for the age-specific relationships between the urinary MnBP, MEOHP, and MEHHP levels and social and attention problems exhibited positive supralinear relationships with downward curvature in the 6-11 year age group. In contrast, the score for social problems exhibited nearly linear relationships with these levels in the 12-18 year age group. In this national sample, increased phthalate exposure exhibited supralinear associations with social, thought and attention problems in children aged 6-11 years, who showed greater vulnerability to phthalate exposure. The results highlight the need for the environmental regulation of phthalate exposure in younger children, even at low dosages.

Young Korean Learners' Usage of the Verb give: Evidence from Their Narratives

The dative alternation in English caused the learnability paradox and many L1 acquisition researchers have dealt with this topic. The purpose of this study was to find out how young Korean learners of English use the verb give and its construction. My arguments are based on the analysis of 11 children``s narratives and their L2 data were collected while each language informant was describing the same wordless picture book, A Circle of Friends by Carmi (2003). The following are the findings: First, it seems that the amount of input bears little or no relation to the usage of the verb give as far as the appropriateness is concerned. Second, 3 informants in the third grade used inappropriate constructions more frequently than appropriate ones (13 versus 7 occurrences). It can be assumed that inappropriate forms like *is give-NP(IO)-NP(DO), *give-NP(DO), or *give-NP(IO), were influenced by their L1. Third, 3 children in Grade 4 began to recognize the verb give as a ditransitive rather than as a transitive, and a prepositional form of the dative alternation was their preference. We can assume that their ill-formed constructions like *is give-NP(DO) (twice), *NP(DO)-and-NP(IO)-is-give, and *NP(DO)-is-NP(IO)-give were the results of L1 transfer. Fourth, 2 children in the fifth grade more frequently used the verb give followed by two objects than the verb followed by a single object (20 versus 12 occurrences). Fifth, it seems that 3 informants in Grade 6 realized the verb give as a ditransitive. The usage of the verb in 2 informants’ narratives was quite appropriate and stabilized, while 1 informant’s narratives showed some characteristics of his Interlanguage. Sixth, it seems that Korean child learners regarded an expression like give me money or give to as a chunk.

Phelan-McDermid syndrome presenting with developmental delays and facial dysmorphisms.

Phelan-McDermid syndrome is a rare genetic disorder caused by the terminal or interstitial deletion of the chromosome 22q13.3. Patients with this syndrome usually have global developmental delay, hypotonia, and speech delays. Several putative genes such as the SHANK3, RAB, RABL2B, and IB2 are responsible for the neurological features. This study describes the clinical features and outcomes of Korean patients with Phelan-McDermid syndrome. Two patients showing global developmental delay, hypotonia, and speech delay were diagnosed with Phelan-McDermid syndrome via chromosome analysis, fluorescent in situ hybridization, and multiplex ligation-dependent probe amplification analysis. Brain magnetic resonance imaging of Patients 1 and 2 showed delayed myelination and severe communicating hydrocephalus, respectively. Electroencephalography in patient 2 showed high amplitude spike discharges from the left frontotemporoparietal area, but neither patient developed seizures. Kidney ultrasonography of both the patients revealed multicystic kidney disease and pelviectasis, respectively. Patient 2 experienced recurrent respiratory infections, and chest computed tomography findings demonstrated laryngotracheomalacia and bronchial narrowing. He subsequently died because of heart failure after a ventriculoperitoneal shunt operation at 5 months of age. Patient 1, who is currently 20 months old, has been undergoing rehabilitation therapy. However, global developmental delay was noted, as determines using the Korean Infant and Child Development test, the Denver developmental test, and the Bayley developmental test. This report describes the clinical features, outcomes, and molecular genetic characteristics of two Korean patients with Phelan-McDermid syndrome.

Behavioral characteristics and parental stress in elementary school children with bronchial asthma and allergic rhinitis

Purpose: The aim of this study was to investigate the differences in behavioral characteristics and parental stress between allergic and nonallergic elementary school children. Methods: Ninety-one elementary school children who had allergic disease were enrolled (asthma, n=27; allergic rhinitis, n=35; combined, n=29). Also one hundred six nonallergic elementary school children were enrolled for the control group. The Korean Child Behavior Check List (K-CBCL) and Korean Parenting Stress Index-Short Form (K-PSI-SF) were completed by their mothers. Results: According to the analysis of K-CBCL, the score for Internalizing, anxious/depressed and somatic complaints were significantly higher in the combined group than in the control group. The score for Diagnostic and Statistical Manual of Mental Disorders (DSM)-affective problems in the combined group and DSM-somatic problems were significantly higher in the asthma group than in the control group. According to the analysis of K-PSI-SF, the score for parental distress was significantly higher in the allergic rhinitis group than in the control group. The scores for behavioral problems and parental stress were significantly correlated to allergic disease groups. Conclusion: Behavioral problems and parental stress were significantly associated with asthma and allergic rhinitis. The results of this study suggest the importance of psychosocial support for mothers and children with allergic diseases. (Allergy Asthma Respir Dis 2016;4:205-211)

Associations between Sugar Intake from Different Food Sources and Adiposity or Cardio-Metabolic Risk in Childhood and Adolescence: The Korean Child-Adolescent Cohort Study.

The increasing prevalence of childhood obesity is a serious public health problem associated with co-morbidities in adulthood, as well as childhood. This study was conducted to identify associations between total sugar intake and sugar intake from different foods (fruit, milk, and sugar-sweetened beverages (SSBs)), and adiposity and continuous metabolic syndrome scores (cMetS) among Korean children and adolescents using cohort data. The study subjects were children (n = 770) who participated in the 4th year (2008) of the Korean Child–Adolescent Cohort Study (KoCAS). Dietary intake data were collected via three-day 24-h food records, and sugar intake was calculated for the total sugar content of foods using our database compiled from various sources. Anthropometric measurements, assessments of body composition, and blood sample analysis were performed at baseline and at follow-up four years later. The cMetS was calculated based on waist circumference, triglycerides, high-density lipoprotein cholesterol, glucose, and mean arterial blood pressure. According to multiple linear regression analysis, there were no significant associations between total sugar intake and adiposity and cMetS. However, higher intake of fruit sugar at baseline was significantly associated with lower body mass index (BMI) z-scores and body fat percentages at baseline (β = −0.10, p = 0.02 and β = −0.78, p < 0.01, respectively). At follow-up, sugar intake from fruit at baseline was still negatively associated with the above outcomes, but only the relationship with BMI z-scores retained statistical significance (β = −0.08, p < 0.05). There was a significant positive relationship between consumption of sugar from SSBs and cMetS at baseline (β = 0.04, p = 0.02), but that relationship was not observed at follow-up (p = 0.83). Differences in consumption sugars from fruit and SSBs might play an important role in the risk of adiposity and metabolic disease in children and adolescents. Our results suggest that strategies for reducing sugar intake need to target particular food groups. Consequently, this information could be of value to obesity- and metabolic disease-prevention strategies.

유아의 가정환경과 또래유능성의 관계에서 언어발달의 역할

본 연구는 가정환경과 만 3세 유아의 언어발달, 그리고 또래유능성 간의 관계를 규명하기 위해 실시되었다. 즉, 유아의 가정환경이 바람직할 때 보다 나은 언어능력의 발달이 가능하며, 이는 어린이집 상황에서 보다 나은 긍정적 또래관계, 그리고 부정적 또래관계의 감소를 예측할 것으로 연구모형을 설정하고 이를 검증하였다. 연구대상은 한국아동패널에 참여하고 있는 유아 800명을 대상으로 하였으며, 이들의 4차년도 자료를 사용하였고, 구조방정식 모델링 기법이 적용되었다. 분석 결과, 가정환경과 유아의 어휘능력은 긍정적인 또래관계와 부정적인 또래관계 행동을 유의하게 예측하였다. 또한 유아 언어발달은 가정환경과 또래유능성을 유의하게 매개하는 것으로 밝혀져 유아의 사회적 관계 형성에 언어발달이 중요한 역할을 하고 있음을 시사한다. The purpose of this study was to investigate the effects of the home environment of young children on their language and the quality of peer competence. The current study hypothesized that when the home environment of young children is desirable, the young children would be more likely to develop better language skills, which in turn, predict greater peer competence and lower levels of aggression and withdrawal in the interaction with peers at child care settings. The study used data of 1,802 families who have been participating in the Korean Child Panel Study since 2008. The results revealed that there was a significant relation from both positive home environment and better language skills to more positive play interaction and reduced play disruption and play disconnection. Home environment significantly predicted better expressive language development of young children and, in turn, higher scores on expressive vocabulary tests predicted greater peer competence and less negative play behaviors rated by child care providers. Statistical tests proved that the mediational effects of language skills between home environment and toddler's peer relationships were statistically significant. The study results emphasized the importance of language development in children's expanding social settings and the supporting role of rich and stimulus home environments in children's development.

부모양육태도와 자아존중감 및 또래애착이 정서문제에 미치는 영향

The purpose of this study was to investigate the effect of Parenting Attitude, Self-esteem, and Peer Attachment on Emotion Problem. The study is based on data from first wave of 'Korean Child Youth Panel Survey 2010(KCYPS)' and the subjects of this survey were 2,098 1st grade junior middle school students. To measure the variables, this study used such scales as the parenting attitude scale, self-esteem scale, and peer attachment scale and emotional problem scale. The data were analyzed using descriptive statistics, Pearson's correlation and structural equation modeling analysis. Results of structural equation modeling with data indicated that hypothesized structural equation model produced a good fit but, no direct effect between negative parenting attitude and peer attachment. The self-esteem have mediating effect between parenting attitude and peer attachment, emotion problem. The peer attachment have mediating effect between positive parenting attitude and emotion problem but, did not have mediating effect between negative parenting attitude and emotion problem. The implications for counseling and suggestions for future research are discussed.

Anger Assessment Using State-Trait Anger Expression Inventory in Middle-School Students in Korea and Association with Depression

Objectives : The purpose of this study was to assess anger of middle school adolescents in an urban community using State-Trait Anger Expression Inventory (STAXI)-Korean and Korean Child Behavior Checklist (K-CBCL), and to determine whether specific anger expression of adolescents is associated with certain psychopathology including depression. Methods : Data were collected from 395 middle school students and their parents in Incheon city. The students completed the STAXI, Children`s Depression Inventory, Korean version of Mood disorder Questionnaire, and Conners-Wells` Adolescent Self-Report Scale (Short Form), and their parents completed the K-CBCL. Results : No significant correlation was observed between aggression subscale K-CBCL and each scale of the STAXI, except anger out (r

The effect of early maternal depression on Korean child’s early vocabulary development

The effect of early maternal depression on Korean child’s early vocabulary development

Crisis Phenomena and the Problems of Disaster Management in Korean Child Care

This study aims to present a view of the Korean child care crisis problems and disaster management. This study diagnosed and analyzed serious risk factors on disaster and safety and provided prospects for future development in this area. Problems and issues of safety-disaster management in Korean child care are 1) discrepancy between policies and fields, 2) problems in laws, 3) problems in administrative management systems, 4) problems in safety educations, and 5) child abuse and SIDS. Further suggestions to overcome these problems are to improve treatment of nursing teachers, amendment of related laws on safety, and development of more applicable and concrete manuals for disaster management.

Directionality study of a Korean child welfare policy through a change process analysis of a Japanese child allowance system

Directionality study of a Korean child welfare policy through a change process analysis of a Japanese child allowance system

The effects of childhood abuse on self-reported psychotic symptoms in severe mental illness: Mediating effects of posttraumatic stress symptoms

The present study examined the role of posttraumatic stress symptoms in the relationship between childhood abuse and self-reported psychotic symptoms in severe mental illness. A total of 126 patients diagnosed with major psychiatric conditions with comorbid symptoms of psychosis participated in the present study. The representative psychiatric diagnoses included schizophrenia, bipolar disorder with psychotic features, major depressive disorder with psychotic features, schizoaffective disorder, schizophreniform disorder, and delusional disorder. The Korean Child Trauma Questionnaire measured the type and degree of childhood abuse including emotional, physical, and sexual abuse. Korean version of the Impact of Event Scale-Revised assessed posttraumatic stress symptoms, and PSYC subscale of the PSY-5 Factor Scale of the MMPI-2 was used as a measure of self-reported psychotic symptoms. There was a significant relationship between childhood physical, emotional, sexual abuse and psychotic symptoms. Posttraumatic stress symptoms partially mediated the relationship between childhood abuse and psychotic symptoms. This implies that childhood abuse is significantly associated with the experience of chronic posttraumatic stress symptoms, and that such symptoms in turn increases the likelihood of experiencing psychotic symptoms. The results highlight the need for appropriate assessment and intervention concerning childhood abuse and posttraumatic stress symptoms in severe mental illness.

Assessment of Children with Language Developmental Delay: Korean Infant and Child Development Test (KICDT) and Preschool Receptive-Expressive Language Scale (PRES), Sequenced Language Scale for Infant (SELSI)

Assessment of Children with Language Developmental Delay: Korean Infant and Child Development Test (KICDT) and Preschool Receptive-Expressive Language Scale (PRES), Sequenced Language Scale for Infant (SELSI)

만4세 유아의 인지발달에 영향을 미치는 생태체계변인 연구

본 연구는 만4세 유아의 인지발달이 생태체계변인에 따라 다른지를 살펴보고, 이 변인들이 유아의 인지발달을 유의하게 예측하는지, 어머니의 취업여부에 따라 상이한 예측을 보이는지를 살펴보았다. 연구대상은 한국아동패널 5차년도 자료인 만4세 유아 998명이었고, 어머니 및 교사 대상으로 질문지 조사를 실시하였다. 그 결과 만4세 유아의 인지발달은 유아성별, 모학력, 부학력, 모취업여부, 가정환경의 질, 자녀기관생활관심정도에 따라 달랐다. 자녀기관생활관심정도가 가장 큰 영향력을 가졌고, 유아성별, 가정환경의 질, 모취업여부의 순으로 인지발달에 영향을 미쳤다. 어머니의 취업여부에 따라서는 다른 양상이 나타났는데, 자녀기관생활관심정도와 성별이 공통적으로 영향력을 미쳤지만 취업모 가정에서 자녀기관생활관심정도의 영향력이 더 크게 나타났고, 가정환경의 질은 취업모 자녀의 인지발달에 대해서만 영향력을 미쳤다. 이 연구결과는 어머니의 취업여부에 따라 유아기 자녀의 인지발달을 도모하는 정책적 접근에 유용한 기초자료를 제공한다. The purpose of this study was to investigate the difference in Korean 4-year-olds' cognitive development depending on variables concerning ecological system variables, predictive influences among these variables, and different predictive patterns between working mothers and non-working mothers. The subjects consisted of 998 4-year-olds, derived from the Korean Child Panel data of 2012. The results were as follows: First, 4-year-olds' cognitive development was different depending on their sex, education level of mother and father, mothers' working status, quality of home environment, and mothers' involvement in children's life in their institution. Second, mothers' involvement in children's life in their institution, children's sex, quality of home environment, and mothers' working status predicted 4-year-olds' cognitive development. Third, there was a different pattern of predictive influence among variables according to the mothers' working status. The mothers' involvement in their children's lives in their institution and children's sex was proved to be important in both, but that was more significant in working mothers, and the quality of home environment predicted cognitive development only in working mothers. These results were discussed in terms of necessity of the Korean national policy to support young children's cognitive development efficiently, especially for working mothers.

The Characteristics of Intellectual and Psychological in the Children with Moyamoya Disease

Purpose: The purpose of this study was to understand the intellectual and psychological features of children with Moyamoya disease who were patients in the Department of Pediatric Neurosurgery of Severance Hospital. Methods: From December 2010 through December 2012, 63 patients with diagnoses of Moyamoya disease and 59 children in a normal group were enrolled. This study was conducted using the Korean-Wechsler Intelligence Scale for Children, Rey-Kim Memory Test for children, Korean Child Behavior Checklist and Pediatric Quality of Life Inventory™4.0. Results: The results showed that the intellectual and psychological profiles of children with Moyamoya disease were lower than the average of the normal control group. The tested patients showed significantly lower scores for Performance Intelligence Quotient cognition level. Also, in terms of quality of life, children with Moyamoya disease had lower levels of physical and school functionality. The results were in line with those of previous studies involving psychological tests of children with chronic diseases. Conclusion: Considering the intellectual and psychological characteristics of children with Moyamoya disease, integrated psychological intervention plans including elements such as supportive therapy for patients and programs for parental education are required. Key words: 모야모야 질환, 인지, ì •ì„œ, 삶의 질 Key words: Moyamoya disease, Intellectual, Psychological, Quality of life

The Effects of Parental Nonstandard Work Schedules on Adolescents’ Academic Achievement in Dual-Earner Households in South Korea

A growing body of research has explored the degree to which nonstandard work schedules affect workers and their families. However, relatively few studies to date have examined the relationship between parental nonstandard work schedules and adolescents’ academic achievement, and even less attention has been paid to Asian populations. This study aimed to examine the effects of parental nonstandard work schedules on adolescents’ academic achievement in South Korea. We analyzed 1100 dual-earner households with middle-school students from the 2011 and 2012 Korean Child and Youth Panel Survey (KCYPS). Results from a cross-sectional ordinary least squares regression and regression with a lagged dependent variable showed that fathers’ nonstandard work schedules were significantly associated with poorer academic achievement in math, while mothers’ nonstandard work schedules were not. In the fixed effects model, however, the negative relationship between fathers’ nonstandard work schedules and adolescents’ academic achievement became only marginally significant. These results provide suggestive evidence that the negative effect of parental nonstandard work schedules on South Korean adolescents’ academic achievement may be due, at least in part, to selection bias. Unobserved differences between standard and nonstandard shift fathers and their adolescents might have biased the estimates from the cross-sectional regression and regression with lagged dependent variable. This implies that future studies on the impact of nonstandard work schedules need to employ robust methods to minimize selection bias.

Effects of GNB3 Polymorphism on Gender Differences along with Energy Intake and HDL Subtypes of Korean Obese Children

The rate of childhood obesity is continuously increasing worldwide, and the similar trend is also shown in a Korean population. A single-nucleotide polymorphism (SNP) C825T in G protein β3 subunit (GNB3) gene is associated with essential hypertension and obesity. However, the potential interaction of GNB3 with food intake and HDL subtype by gender in Korean child obesity has not been closely evaluated yet. In this study, we analyzed data collected from 635 boys and 627 girls of the 3rd grade elementary school children in Seoul, Korea. Relative frequencies of wild type on GNB3 SNP C825T were 51% and 49.4 % in boys and girls. Boys with GNB3 T allele had significantly higher body weight, BMI, WC compared to those of boys with C allele. On the other hand, girls with GNB3 C allele had significantly higher body weight, BMI, WC, ALT compared to those of girls with T allelle. Plasma visfatin, a visceral fat derived hormone, were significantly higher in boys with C allele. Girls with T allele had higher energy intake compared to girls with C allele whereas there was no difference of energy intake between boys with T allele and boys with C allele. Finally, the HDL peak size was lower in T allele compared to C allele suggesting inefficient reverse cholesterol transport by HDL in children with T allele. Therefore, GNB3 polymorphism plays an important role to affect children obesity rate, energy intake, HDL peak sizes in Korean children. [This work was supported by Korea Food Research Institute, Mid-career Researcher Program through NRF grant fund(MEST; 2010-0000147).]

The Risk of Overweight and Insufficient Dietary Intake among Children in Low‐income Family in South Korea

AimsObesity prevalence has increased steadily in Asian countries. Especially low‐income child is known as vulnerable to obesity due to the limited access to affordable foods and health care. To identify the health and nutrition condition of low‐income children in South Korea, data from the fifth Korean National Health and Nutrition Survey(2010‐2012) was used. Methods: To define the risk of children's health and nutrition status, we adapted the classifications of the Korean family income level(The National Statistical Office, 2012), Korean child standard growth charts(KCDC, 2007), and Korean nutrition intake standards(The Korean Nutrition Society, 2010). Data from age 1 to age 5(n=2,272,243) were analyzed by survey module in SAS. Results: The children's overweight risk decreased by family income. 13.6% children in family with the minimum cost of living were over 95percentile in BMI. However their undergrowth(&lt;5percentile in BMI) rate is the lower(2.2%) compared with other income groups. Those children in the lowest income group had the highest percent of inadequate intake of carbohydrate and fat among children(52.4%, 44.0%). They also had largest rate of insufficient intakes in Vitamin A(37.5%), B1(20.0%), B2(23.9%), Niacin(29.5%), Vitamin C(43.1%), Calcium(64.7%), and iron(41.2%).ConclusionsFor the healthy growth among children in low‐income families in South Korea the accessibility of healthy foods and health care are need to be secured.

Cultural Adaptation and Translation of Outreach Materials on Autism Spectrum Disorder.

In order to connect with families and influence treatment trajectories, outreach materials should address cultural perceptions of the condition, its causes, and post-diagnostic care. This paper describes the cultural adaptation and translation of the Autism Speaks First 100 Days Kit into Korean for the purpose of improving autism spectrum disorder (ASD) diagnosis, assessment, and interventions. The goal of this study is to describe a methodology for future cross-cultural adaptations and translations of outreach materials on ASD, using the Autism Speaks First 100 Days Kit as an exemplar. The research involved two stages of qualitative interviews: unstructured individual and group interviews with 19 Korean child health and education professionals in Queens, NY, followed by structured cultural consensus modeling interviews with 23 Korean mothers, with and without children with ASD, in Queens, NY and the greater Washington, DC area. We conclude that a systematic approach to cultural translation of outreach materials is feasible. Cultural consensus modeling yielded information about numerous barriers to care, had a demonstrable effect on the translation of the kit, and was efficient when employed with coherent segments of a relatively homogeneous population and focused on a single condition.