Data for children aged 2 to 7 years (n = 5200) and 8 to 16 years (n = 3996) were analyzed from NHANES III, a cross-sectional representative sample of the US civilian noninstitutionalized, nonhomeless population living in households. The survey was conducted from 1988 to 1994. Mexican Americans and black Americans were oversampled to provide more reliable estimates for these groups. Detailed descriptions of the sample design and operation of the survey have been published elsewhere.34 Data from NHANES III included medical examination results and interviews conducted with survey participants and proxies who were parents or other relatives or caretakers familiar with the child. All interviews and examinations were conducted using standard protocols.34
CONCEPTUAL FRAMEWORK
Using past research, a conceptual framework of the factors affecting children's body mass index was created using available variables from NHANES III35- 45 to guide the analyses in this study. This framework is shown in Figure 1. We postulate that having fewer family resources can lead to food insufficiency, health care risks, or exercise risks that can affect a child's body mass index. Family resources that could be associated with food insufficiency, health care risks, and/or overweight include family income, measured as the poverty-income ratio (PIR), education of the family head, marital status of the family head, family size, and whether the child lives in a metropolitan region. Health care risks include lack of health insurance or a regular source of health care. For older children, exercise risks include increased number of hours spent watching television or lack of physical activity. Past health and nutrition risks can also affect the child's body mass index. These include the child's birth weight, whether the child had birth complications, whether the child was exposed to smoke prenatally, and/or short stature. Hereditary factors can also affect a child's body mass index, which we controlled using parental height and weight.