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* Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853-6301 and Center for Research in Nutrition and Health Disparities, University of South Carolina, Arnold School of Public Health, Columbia, SC 29204
3 To whom correspondence should be addressed. E-mail: eaf1{at}cornell.edu.
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ABSTRACT |
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 TOP ABSTRACT SUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • food insecurity • child development • overweight • academic • longitudinal
Household food insecurity is associated with adverse outcomes in children and adolescents, including inadequate nutrient intake, overweight or greater weight gain, poor school performance and academic delays, and poor social functioning and behavior problems (1). U.S. federal food assistance programs such as the Food Stamp Program (FSP)4 aim to help prevent household food insecurity and its outcomes. The FSP serves to help low-income households obtain a more nutritious diet by increasing their purchasing power. Over half of food stamp recipients are children aged 17 and under (2). Families are eligible if their gross income is <130% of the poverty line, they have less than $2000 in savings or investments, and they meet work requirements. Such households are provided with cash equivalents to equal about 70% of their estimated food budget to purchase food to be prepared at home. In 2004, the program served about 24 million people per month with an average monthly food stamp benefit of about $200 per household (2). Total cost to the federal government in 2004 was nearly $25 billion.
Program participation is an elective behavior, making it difficult to distinguish between causal effects of the program and selection effects of the choice to participate (3). Cross-sectional data cannot untangle the complex relations among food insecurity, program participation, and developmental outcomes. Absent a randomized design, longitudinal data provide the best means to establish that observed effects are causal and not the result of confounding, selection bias, or reverse causality (4).
Most researchers have assumed that program participation reduces food insecurity or malnutrition, thereby improving outcomes. An alternate conceptualization, however, considers food insecurity or material hardship to be a stressor (5,6). In this conceptualization, program participation acts as a resource to either counteract the effects of resource constraints such as food insecurity or to modify the effects of food insecurity on outcomes. Prior evidence for a modifying role of food assistance comes from a study reporting reduced risk of overweight among food-insecure girls participating in the FSP and National School Lunch Program compared with nonparticipating food-insecure girls (7). To our knowledge, no studies have investigated using longitudinal data whether FSP participation acts as a modifier between food insecurity or material hardship and child outcomes.
This study aimed to determine relations among participation in the FSP, household food insecurity, and selected dimensions of children's academic, social, and physical development over 4 years using a prospective longitudinal study design and modeling techniques that minimize bias. We investigated 1) whether changes in FSP participation were associated with changes in child reading and mathematics performance, social skills development, and weight gain, while controlling for changes in food insecurity and other covariates, and 2) whether FSP participation modified the relationships between need for food assistance and these outcomes.
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SUBJECTS AND METHODS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Parents were asked whether anyone in the household had received food stamps in the past 12 mo. To capture changes in FSP participation over time, a continuous variable was computed as the difference between the dichotomous values representing FSP participation at K and third grade, where starting participation was coded as 1, stopping participation as –1, and no change in participation as 0.
Household food insecurity was measured using the USDA's Household Food Security Survey Module, an 18-item scale designed to capture experiences associated with inadequate quality and quantity of the household food supply within the past 12 mo (9). The USDA module was administered to parents by written survey in the spring of 1999 and the spring of 2002. Households that affirmed 1 or more items were classified as food insecure.
Food insecurity is a measure of the extent to which families are able to meet their basic needs, i.e., the extent to which families experience material hardship (10). Most poor families face multiple hardships (11). Because food insecurity alone may be insufficient for capturing hardships that federal assistance programs intend to address, a composite "need" measure was created (10,12). Rotated factor analysis determined that the following 4 variables loaded onto 1 factor: 1) lower education level of either parent, 2) lower household poverty index ratio category, 3) absence of a home computer, and 4) food insecurity. Z-scores for each variable (K and third grade) were computed, weighted according to K factor loadings, and averaged into composite "need" scores, with separate scores generated for K and third grade. A higher value indicated greater "need" or material hardship. Change in "need" was computed by subtracting kindergarten scores from third grade scores. Higher difference indicated a greater increase in need.
Mathematics and reading performance were assessed in K and third grade. The mathematical test measured understanding of properties of numbers, mathematical operations, problem-solving, understanding of patterns and relationships among numbers, formulating conjectures, and identifying solutions. The reading test measured basic literacy, vocabulary, and reading comprehension (9). Scaled scores were calculated using item response theory. Mathematics scores ranged from 0 to 123, and reading scores from 0 to 154.
Children's heights and weights were directly assessed at both K and third grade. Each was measured twice to minimize measurement error, and the mean of each set of values was used (9).
Children's social skills were assessed by teacher questionnaires (13). Teachers rated how often their students exhibited certain social behaviors on a scale of 1 (never) to 4 (very often), for a variety of behaviors within each of 4 overall scales. Three of the scales captured positive aspects of children's development: approaches to learning, self-control, and interpersonal skills. The other scale captured externalizing (i.e., acting-out) problem behaviors. We averaged the individual scales to create a composite social skills behavior score.
Preliminary analyses showed nonnormal distributions for change in weight, change in height, initial mathematics score, and initial reading score. Logarithmic transformations of these variables were used. Means and regression coefficients are reported after back-transformation.
Multiple linear regression was used to test for differential effects in changes for 4 child developmental outcomes of interest: mathematics score, reading score, weight, and social skills score. The SAS surveyreg procedure (14) was used to account for effects of survey clustering, primary sampling units, and sample weights. Each outcome was analyzed using a difference, i.e., fixed-effects, model (15). Change in development score was modeled as a function of changes in time-varying covariates, difference in food insecurity or composite need over time, and difference in FSP participation over time:
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where the subscripts 3 and k refer to the time of assessment (third grade or kindergarten), FSPP refers to FSP participation, and FIS refers to food insecurity status. The same model was run including an interaction term and substituting composite need for food insecurity:
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where NEED refers to the continuous composite measure of material hardship. The difference model removes individual fixed effects and eliminates the influence of time-invariant unobserved (and observed) heterogeneity by differencing out effects of factors that that remain unchanged over time and focusing entirely on transitions. We accounted for time-varying heterogeneity by controlling for as many relevant child- and household-level time-varying covariates as possible. The covariates included in the analyses are listed in footnotes to Table 1. Continuous covariates were entered into the model as differences over time. Categorical variables were entered into the class statement, with 0 representing no change from kindergarten to third grade and each level other than 0 representing a change in status (e.g., 1 = became divorced, 2 = became married, 3 = became widowed). This model theoretically gives the least biased estimates of association (15), assuming there is a short lag between starting or stopping the FBP and its effect on child development relative to the duration of time between measurements. This model can be claimed to be causal only if effects are able to play out temporally.
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RESULTS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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From K to third grade, children in households that started FSP participation had a 3-point greater change in both reading and mathematics score than did children in households that stopped FSP participation (Table 1). All (for reading) or most (for mathematics) of this effect was for female children. There were no differences in change in weight or social skills score with change in FSP participation.
Changes in need for food assistance did not modify the relationships between change in FSP participation and changes in these outcomes (results not shown). In comparisons between the first and the third quartiles of change in need, all the differences in the relationships between change in FSP participation and changes in outcomes were <1.0 in magnitude and had P-values >0.18.
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DISCUSSION |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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With other factors controlled, starting FSP participation during the 4 years from K to third grade was associated with about a 3-point greater improvement in reading and mathematics score as compared with stopping FSP participation during that period. However, it was for female students only that this association was large and significant. Female students had greater improvement of 5.9 points in reading score and 3.4 points in mathematics score for starting versus stopping FSP participation. These differential improvements in starting versus stopping FSP participation for female students correspond to effect sizes of 0.36 for reading and 0.27 for mathematics; that is, these differences were about one-third of a standard deviation in changes in scores.
Although concerns have been raised about possible effects of the FSP on promoting excess weight gain (4), this study found to the contrary that children in households starting FSP participation had slightly but not significantly less weight gain compared with children in households stopping FSP participation. These results are consistent with other recently findings that FSP participation was associated with either lower or equal risk of overweight for children (7,16).
FSP participation could affect academic learning through improving the quantity or quality of dietary intake. The FSP increases household food expenditures, food energy, and protein and "may also increase the availability of a number of vitamins and minerals" (17). But there is "little evidence that the FSP consistently affects participants' dietary intakes" (17).
The accumulating evidence that food insecurity has multiple outcomes that are both nutritional and nonnutritional in nature is consistent with an understanding that food insecurity acts as a stressor on households. Both biological (18) and environmental stress (19) have been linked to cognitive performance. FSP participation may therefore act as a financial or social resource to counter the effects of stress resulting from food insecurity or other material hardship.
In conclusion, the results of this study provide the strongest evidence to date that FSP participation plausibly has beneficial effects for children on nonnutritional outcomes, specifically academic learning during the first 4 years of school. The mechanisms for this relationship are not well elucidated and may be through both dietary intake and stress. The FSP should be understood as a means of enhancing academic performance and learning among school children as well as enhancing food expenditures and access.
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FOOTNOTES |
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2 Supported by cooperative agreement 43-3AEM-3-80104 with the United States Department of Agriculture Economic Research Service.
4 Abbreviations used: ECLS, Early Childhood Longitudinal Study-Kindergarten cohort; FSP, Food Stamp Program.
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LITERATURE CITED |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Jyoti DF, Frongillo EA, Jones SJ. Food insecurity affects school children's academic performance, weight gain, and social skills. J Nutr. 2005;135:2831–9.
2. Poikolanen A. Characteristics of food stamp households: fiscal year 2004, FSP-CHAR. Alexandria, VA: U.S. Department of Agriculture, Food and Nutrition Service, Office of Analysis, Nutrition, and Evaluation, Project Officer, Kate Fink, 2005.
3. Frongillo EA. Understanding obesity and program participation in the context of poverty and food insecurity. J Nutr. 2003;133:2117–8.
4. Frongillo EA, Rowe EM. Challenges and solutions using and analyzing longitudinal growth data. In: Johnstone FE, Eveleth P, Zemel B, editors. Human growth in context. London: Smith-Gordon, 1999. pp. 51–64.
5. Ensel WM, Lin N. Age, the stress process, and physical distress. J Aging Health. 2000;12:139–68.
6. Hamelin AM, Beaudry M, Habicht JP. Characterization of household food insecurity in Quebec: food and feelings. Soc Sci Med. 2002;54:119–32.[Medline]
7. Jones SJ, Jahns L, Laraia B, Haughton B. Lower Risk of overweight in school-aged food insecure girls who participate in food assistance: Results from the Panel Study of Income Dynamics Child Development Supplement. Arch Pediatr Adolesc Med. 2003;157:780–4.
8. National Center for Education Statistics. ECLS-K longitudinal kindergarten-third grade public-use data file [CD-ROM]. Washington, D.C.: U.S. Department of Education, Institute of Education Sciences, 2004.
9. Bose J, West J, Tourangeau K, Nord C, Le T, Wan S. User's guide to the longitudinal kindergarten-first grade public-use data file. Washington, D.C.: U.S. Department of Education, Office of Educational Research and Improvement, NCES 2002–149, 2002.
10. Oullette T, Burstein N, Long D, Beecroft E. Measures of material hardship. Final report. Washington, DC: U.S. Department of Health and Human Services, 2004.
11. Sherman A. Hunger, crowding, and other hardships are widespread among families in poverty. Washington, D.C.: Center on Budget Policy and Priorities, December, 2004.
12. Lee JS, Frongillo EA. Understanding needs is important for assessing the impact of food assistance program participation on nutritional and health status of U.S. elderly persons. J Nutr. 2001;131:765–73.
13. Gresham FM, Elliott SN. Social Skills Rating System. Circle Pines, MN: American Guidance Service, 1990.
14. SAS Institute Inc. SAS version 8.2. Cary, NC, 1999: SAS.
15. Cawley J. The impact of obesity on wages. J Hum Resour. 2004;39:451–74.
16. Hofferth SL, Curtin S. Do food programs make children overweight? College Park, MD: Department of Family Studies, University of Maryland, 2004. <www.popcenter.umd.edu/people/hofferth_sandra/papers/food_childoverweight.pdf>
17. Fox MK, Hamilton W, Lin BH. Effects of food assistance and nutrition programs on nutrition and health: volume 4, Executive summary of the literature review. Washington, D.C.: Food and Rural Economics Division, Economic Research Service, U.S. Department of Agriculture, Food Assistance and Nutrition Research Report No. 19–4, 2004.
18. Lupien SJ, Fiocco A, Wan N, Maheu F, Lord C, Schramek T, Tu MT. Stress hormones and human memory function across the lifespan. Psychoneuroendocrinology. 2005;30:225–42.[Medline]
19. McLoyd VC. Socioeconomic disadvantage and child development. Am Psychol. 1998;53:185–204.[Medline]
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