Data Sources
Data were obtained from the Early Childhood Longitudinal Study (ECLS-K), which followed children from kindergarten (1998-99 school year) through the 2007 school year, when most children were expected to be in eighth grade. The 1998-99 class cohort was a nationally representative sample of kindergartners, parents, teachers, and schools from across the US. The Institutional Review Board at Indiana University verified the current study as a non-human subject study. Participants included in data analyses represent all waves of data collection time points (i.e., school years 1998-99, 1999-2000, 2001-02, 2003-04, and 2006-07). Dropouts and subjects added to the sample at any time are not included in the current study.
Conceptual Framework
The modified socioecological framework [14] was used as the conceptual basis of the current study, as this model incorporates key transitions in children’s lives. Because child data was nested in parent, family, and environmental settings, a multilevel research approach was needed to account for the significant implications of the hierarchical structure [14]. This approach encompasses the primary needs of children, parents, families, and community members related to childhood development. The assessment framework consists of three parts: (a) individual needs (i.e., health, education, emotional/behavioral development, identity, family, social relationships, social presentation, and self-care skills); (b) parenting capacity (i.e., basic care, ensuring safety, emotional warmth, stimulation, guidance, boundaries, and stability); and (c) family/environmental factors (i.e., community resources, family’s social integration, income, employment, housing, extended family, and family history and functioning).
Measures
Outcome Variables. BMI percentile was the main outcome variable in this study, which was calculated and categorized as follows. First, BMI was calculated as weight in kilograms divided by square of height in meters and considered in relation to age and gender [15] Then, BMI percentile was used to determine severity of childhood obesity. Four levels of childhood obesity were categorized in this study: normal weight (BMI 5th–85th percentile); overweight (BMI 85th–95th percentile); obesity (BMI equal to or greater than the 95th percentile); and severe obesity (BMI equal to or greater than the 99th percentile) [4, 6, 8].
The secondary goal of the current study was to examine the role of socioecological obesogenic factors when children transition from normal/healthy weight to being overweight, obese, or severely obese. From the main outcome variable of BMI, transitions among the four main levels of a child’s weight severity were recorded on a 7-point scale (from -3 to 3). In this scale, 3 was considered “worsening,” recording three levels of worsening of BMI status from Wave 1 to Wave 2 (e.g., normal at Wave 1 to severely obese at Wave 2). Conversely, -3 was considered “improving,” meaning that a child improved BMI from Wave 1 to Wave 2 (e.g., severe obesity at Wave 1 and normal body weight at Wave 2). A score of 0 represented no change in BMI between the two waves.
The objectives of this study were based on similar studies that have identified the relevant obesogenic independent variables and examined how socioecological factors influence BMI status and transitions in children. Thus, the same independent variables were employed.
Independent Variables. Individual obesogenic variables included gender, ethnicity, age, amount of computer usage, and number of hours watching TV after dinner. Ethnicity was categorized into four groups: Hispanic, non-Hispanic white, non-Hispanic black, and other. The amount of computer usage was indicated by the number of times per week measured on a 4-point scale from 1 (Never) to 4 (Daily). The number of hours watching TV after dinner was assessed by the average number of hours spent watching TV or videos at home each day following the final meal of the day (range = 0–7 hours).
Parental variables related to childhood obesity consisted of parental educational levels, mother’s weekly working hours, and parental involvement. The highest level of education of the head of household was assessed on a 9-point scale from 1 (8th grade or below) to 9 (Doctorate or professional degree). Mother’s working hours were measured by current employment status on a 4-point scale from 1 (Not in the labor force) to 4 (35 hours or more per week).
Family functioning consisted of a single-parent variable, number of family members less than 18 years old, child’s primary caregiver, a poverty indicator, income level, TV restrictions at home, and food security. There were five categories of combined family structure associated with a child’s parent(s), which were restructured as a binary variable (e.g., two-parent family vs. other family structure). Previous studies have shown that the health status of children with two parents may differ from that of children who are from different family structures [16, 17]. Additionally, a 7-point scale for types of primary care was utilized, and restructured as a binary variable, with “0” representing non-parental care and “1” representing parental care, as children with parental care may show different health outcomes compared to those who are cared for by someone else [18-21]. Number of family members under 18 and household size were measured as a range of 1–11 and 2–17, respectively. Nine classification categories for the child’s primary caregiver living in the household were measured, and restructured as binary variables, including biological mother and father vs. other, because children cared for by biological parents may show different health outcomes [21-23] According to the US Census Bureau [24], a binary variable for poverty threshold was assessed in accordance with family size and number of children. Level of income was measured on a 12-point scale from $5000 or less to $200,001 or more. Additionally, the level of income was categorized into quintile indicators to secure an unbiased measurement of income level. To measure TV watching restriction for children, a binary variable for a family’s rule regarding TV was assessed. Finally, food security in the household was measured on a 4-point scale from food insecure with hunger to food secure.
One of the key environmental obesogenic factors in childhood obesity is school [25]. School environmental factors consist of three main variables: type of school, proportion of minority students, and proportion of students eligible for free or reduced lunch. The percentage of minority students was assessed on a 5-point scale from 1 (Less than 10%) to 5 (75% or more). To measure the proportion of students eligible for reduced lunch, a 5-point scale was used to assess percentage of student eligibility from 1 (Less than 1%) to 5 (25% or more). Lastly, urbanity level of where children live was measured as an obesogenic factor. The characteristics of children’s geographical residence were divided into three categories of urbanity: large city, mid-size city, and small town/rural area of a large city.
Statistical Analyses
Unweighted and weighted descriptive statistics of the sample were determined to describe demographic characteristics, such as age, gender, ethnicity, and BMI status, in terms of means, standard deviations, or percentages. Pearson’s χ2 tests and t-tests with weighted counts and column percentages were used to compare descriptive statistics. Two longitudinal ordered logistic regressions were used to examine associations between sociodemographic variables (e.g., family activities, parents’ health behavior), obesity status, and transition across all waves, respectively. First, a longitudinal ordered regression was performed to examine the associations between BMI status (i.e., normal, overweight, obese, and severely obese) when controlling for sociodemographic variables. Further, a longitudinal ordered regression (i.e., recovery, maintained weight, and worse BMI changes), which is a panel regression with a random effect, was performed to capture factors influencing children’s weight transitions across time waves, controlling for demographics, physical activity-related behaviors, and familial/environmental conditions. Stata® 15.0 and SAS version 9.4 were utilized for all statistical procedures, with a .05 alpha level and a 95% confidence interval.