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Posted on March 28th, 2013, by

Research questions and actuality
Childhood obesity rates have dramatically increased during the recent 30 years: in 1980 the rate of obese or overweight children between the ages of 6 and 11 years old was 6.5%, and in 2004 this rate increased to 18.8% (Franzini et al., 2009). Child obesity is the cause of many physical and mental problems, which can persist into adult obesity and related diseases. The issues of childhood obesity are thus highly important for nursing and health care professionals as well as development of methods and policies against childhood obesity.

The article Influences of physical and social neighborhood environments on children’s physical activity and obesity is devoted to the investigation of the relation between social and physical neighborhood environments and the levels of physical activity and obesity of fifth-grade students. The research hypothesis states that physical activity levels, correlating with childhood obesity, are negatively associated with the changes of physical environment, expressed as more traffic, more physical disorder, low residential density and primarily residential neighborhood (Franzini et al., 2009), and are positively associated with the social environment (measured as social cohesion and safety) (Franzini et al., 2009).

The researchers analyzed the factors which may contribute to childhood obesity at both individual and contextual level, and have outlined several groups of factors. At individual level, sociodemographic characteristics of the child are important, and at the contextual level factors were organized into two groups: neighborhood physical and social environment. Previous studies have focused mostly on the factors relating to the physical environment. Thus, the research by Franzini et al. (2009) is highly important for health care professionals, since it outlines critical factors causing low levels of physical activity and allows to develop policies and interventions for reducing childhood obesity.

Research data was collected as part of the Healthy Passages study Phase 1, which is a cross-sectional study of children’s health. The sample includes data collected for 650 fifth-grade students and for one of their primary caregivers (one of the parents, in most cases). Data were gathered between May and September 2003 at the University of California (Los Angeles), the University of Alabama (Birmingham) and the University of Texas Health Sciences Center (Houston) (Franzini et al., 2009). The final sample includes 205 Hispanics, 236 non-Hispanic Blacks, 157 non-Hispanic

Whites and 52 representatives of other racial/ethical groups.
The size of the sample can be considered representative for a large population, and is reliable both for the population of fifth-graders and for the population of children of school age. This conclusion is based on the estimates using the formula for determining minimal sample size: , where n is the minimal size sample, N total size of the population, d precision level, Z the number of standard deviation units of the sampling distribution corresponding to the desired confidence level (Jackson, 2011).

In 2003, the number of elementary school students (grades 1 through 4) constituted 15.9 million, elementary school students (grades 5 through 8) 16.6 million and high school (grades 9 through 12) 17.1 million (U.S. Census Bureau School Enrollment, 2011). Thus, N is approximately 4.15 million for the population of fifth graders, and 49.6 million for the whole school students. Acceptable precision level is 0.05, and Z-factor for this precision level is 1.96 (Jackson, 2011). According to the formula for minimal sample size, for both populations n=385. Thus, the sample containing 650 participants is appropriate for the chosen population with a precision level of 0.05, or with 95% confidence.

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