Table 3.
Study, Population Characteristics, and Main Results for BMI Outcomes of Natural Experiment Studies With Low or Medium Risk of Bias
| Study characteristics | Baseline population characteristics within studies | |||||||
|---|---|---|---|---|---|---|---|---|
| First author, year, country | Program level; policy or built- environment change | Comparator group | n | Age or grade, range | Female, %, range | Race, %, range | Analysis, study length | Main result for BMI outcomes |
| Capogrossi, 2017, U.S.21 | Federal; participation in both the School Breakfast Program and National School Lunch Program | Participation in both programs versus only the National School Lunch Program | 3,020 | Grades 1–8 | 45–57 | Black, 7–33 Hispanic, 17–26 |
DID and ATT, 8 years | Increased probability of being overweight with participation in both meal programs |
| Hennessy, 2014, U.S.22 | State; competitive food laws in schools | Strong food laws versus weak food laws versus no law (reference) | 16,271 | 11–14 years old | 51 | White, 64–47 Black, 14–21 Hispanic, 15–25 Other, 8–7 |
Regression model, 2 years | Increased odds of overweight/obesity Weak laws: OR=1.23, 95% CI=1.05, 1.45 Strong laws: OR=1.01, 95% CI=0.798, 1.30 |
| Heelan, 2015, U.S.23 | Local; district- and school-level implementation of physical education grant program, healthier school meals, school wellness, and BMI screening | Pre-implementation versus post-implementation | 2,244 | Grades K–5 | NR | White, 85 | Pre–post, 6 years | Decreased prevalence of overweight or obesity, from 16.4% to 13.9% |
| Schwartz, 2016, U.S.24 | Local; implementation of water jets in schools for dispensing cooled water | Schools with versus without water jets | 1,065,562 | Grades K–8 | 50 | Asian, 12–14 Black, 33–36 Hispanic, 37–39 White, 13–14 |
DID, 5 years | Reduced BMIz in boys: OR= −0.025, 95% CI= −0.038, −0.011; in girls: OR= −0.022, 95% CI= −0.035, −0.008 |
| Fitzpatrick, 2017, Canada25 | Local; Dietary environment in the school as well as in the surrounding neighborhoods | Healthful versus unhealthful food environments | 431 | 8–12 years | 42–49 | White, 100 | Regression model, 2 years | No difference in BMIz Mean change= 0.06, 95% CI= −0.16, 0.28 |
| Nanney, 2016, U.S.26 | Local; policies around foods available in school vending machines and stores; PE requirements, intramural sports | Pre-implementation versus post-implementation | 7,237 | Grade 9 | NR | Minority, 10–14 | Regression model, 6 years | BMI% +0.01 (95% CI=0.00, 0.02) when less healthy food available |
| Goldsby, 2016, U.S.27 | Local; construction of a new neighborhood park | Pre- versus post- construction of park | 1,443 | 2–17 years | 56 | Black, 78 White, 22 Hispanic, 14 |
Pre-post, 1–3 years | Increased BMIz Mean change= +0.03, p= 0.0007 |
| Madsen, 201128 | Other; BMI screening with parental notification of BMI | Parental notification versus no parental notification | 755 | Grades 5, 7, 9 | NR | Black, 9 White, 33 Hispanic, 40 |
Regression model, 7 years | No difference in BMIz Mean change= −0.01, 95% CI= −0.03, 0.01 |
ATT, average treatment effect in the treated; BMI%, BMI percentile; BMIz, BMI z-score; DID, difference in difference; K, kindergarten; NR, not reported; PE, physical education.