Pediatric Weight Management

PWM: Environment (2012)


Liu GC, Wilson JS, Rong Q, Ying J. Green neighborhoods, food retail and childhood overweight: Differences by population density. Am J Health Prom; 2007. 21 (Supp): 317-325.

PubMed ID: 1746517
Study Design:
Cross-Sectional Study
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine relationships between two environmental factors:

  • Greenery surrounding a child's residence
  • Proximity of the residence to fast food restaurants to overweight status.
Inclusion Criteria:
  • Age three to 18 years
  • Resident of Marion County, Indiana
  • Seen for routine well-child care at one of seven urban primary care clinics in Indianapolis, Indiana during the year 2000; diagnosis verified by ICD-9 codes.
Exclusion Criteria:
  • Pregnancy, congenital heart disease, chromosomal abnormalities, anomalies of the adrenal gland, cystic fibrosis, cerebral palsy, and multiple congenital anomalies
  • Home address not located in Marion County, Indiana.
Description of Study Protocol:


Children's records obtained through an electronic medical record system


Subjects addresses were geocoded for the two environmental factors of interest and linked with BMIs.

Blinding used

Not applicable



Statistical Analysis

  • Two-sample t-tests used to compare means between high- and low-population density areas
  • Pearson chi-square used to compare frequencies between high- and low-density population areas
  • Cumulative logit model used to associate overweight with population density (high or low).
Data Collection Summary:

Timing of Measurements

Greenery assessed in July 2000; population data from 2000 US Census; patient data from 2000 calendar year.

Dependent Variables

  • BMI: Assessed using 2000 CDC tables and cutoffs, then categorized into four groups
    • Group 4: BMI >98th percentile
    • Group 3 BMI >95th percentile
    • Group 2 BMI >85th percentile
    • Group 1: All others.

Independent Variables

  • Township population density: Patient addresses geocoded using street centerline files from the Indianapolis Mapping and Geographic infrastructure System with supplementation from ArcGIS 9.0TM. 98% of patients were successfully geocoded; those who were not did not differ by age, race, gender, or insurance from those who were geocoded. Three categories created:
    • Sparsely populated zero to 149 persons per square mile
    • Moderately populated 150-695  persons per square mile
    • Densely populated 695 persons per square mile
  • Neighborhood vegetation, obtained from Landsat Enhanced Thematic Mapper Plus satellite imagery. Normalized Difference Vegetation Index values range from -1(usually water) to +1(dense healthy green vegetation). Reference points: Moderate vegetation (0.2-0.3) shrubs and grassland, tropical rainforests (0.6 to 0.8). Calculated for each participant using a 2-km circular buffer with subjects' home at the center.
  • Food retail location and hygiene grading from Marion County Health Department; classified using 1997 North American Industry Classification System and codes into
    • Large brand-name supermarkets
    • Smaller non-brand-name grocery stores
    • Fast food restaurants
    • Convenience stores
  • Distance from subjects' homes to food retail locations was determined using street centerlines.
  • Neighborhood-level socioeconomic status: Median family income per city block in 2-km buffer around each child's residence, using Census 2000 data. 

Control Variables

  • Age
  • Race, ethnicity, categorized as Black, Hispanic, White, other
  • Gender.


Description of Actual Data Sample:
  • Initial N: 7,334 children
  • Attrition (final N): Not applicable
  • Age: Mean age eight years
  • Ethnicity:
  • Other relevant demographics: The study area was divided into  Higher Population Density Townships, consisting of of six townships that had a population density with a mean of 2,637 persons per square kilometer. Three townships were classified as Lower Population Density with a mean of 1,083 persons per square kilometer. The mean population density was different between the two groups, P=0.02.
  • Anthropometrics: See results
  • Location:  Marion County, Indiana, USA.


Summary of Results:

Key Findings

  • Increased amounts of vegetation surrounding a child's home was associated with lower risk of overweight in Higher Population Density townships
  • Distance to the nearest grocery store or supermarket decreased the risk of obesity in Higher Population Density townships
  • No environmental variables influenced obesity risk in Low Population Density townships.

Summary of Age, Neighborhood Income and Envrionmental Indices by Township Population Density

Variables Higher Density Lower Density P
Age, years 8.06±3.78 8.12±4.02 0.76
Neighborhood median family income, $1000s 40.20±10.29 52.7±8.55 <0.01

Normalized Vegetation Difference Index

0.11±0.08 0.13±0.08 <0.01
Distance to nearest food retail 2.36±1.6 3.56±2.54 <0.01
Distance to nearest grocery store, km 4.58±3.54 6.72±5.14 <0.01
Distance to nearest fast food restaurant, km 3.25±1.85 4.56±3.08 <0.01
Distance to nearest supermarket, km 7.12±3.93 6.77±5.31 0.07
Distance to nearest convenience store  3.00±1.79  4.19±3.12 <0.01

Race/Ethnicity, Gender, and Weight Status Distributions by Township Population Density 

Variable   Higher Density, % Lower Density,%
Race/ethnicity White 22.8 21.1
  Black 60.7 45.1
  Hispanic 14.9 28.2
  Other 1.7 5.7
  P <0.01  
Gender Male 49.1 45.6
  Female 50.9 54.4
  P 0.15  
Overweight Index BMI ≤85% 60.2 61.3
  85% 17.3 16.7
  95% 9.2 8.7
  BMI>98% 13.3 13.3
  P 0.96  


Summary of Factors and Predictors in the Cumulative Logit Model

Variable P
Township population density 0.24
Gender 0.86
Race/ethnicity <0.01
Age <0.01

Neighborhood median family income

Gender x population density 0.68
Race/ethnicityx population density 0.36
Age x population density 0.77
Median family income of neighborhood x population density 0.31

Older children had a higher risk of overweight.

Age, neighborhood income, and Race/ethnicity Co-variates for Cumulative Logit Model

Variable   mean, SE P mean, SE P mean, SE P
Age   0.06±0.01 <0.01 0.07±0.01 <0.01 0.05±0.02 0.03
Neighborhood median family income, $1000s   -0.06±0.02 <0.01 -0.07±0.01 <0.01 -0.002±0.12 0.99
Race/ Ethnicity Black -0.23±0.06 <0.01 -0.24±0.06 <0.01 -0.07±0.25 0.79
  Hispanic 0.021±0.07 <0.01 0.20±0.08 <0.01 0.3±0.27 0.25
  Other 0.14±0.17 0.41 0.03±0.18 0.88 -0.66±0.51 0.18±


Author Conclusion:

The authors conclude that this study adds to the body of literature suggesting that the built environment affects health behaviors and outcomes.

Funding Source:
University/Hospital: Indiana University School of Medicine; Indiana University-Purdue University Indianapolis
Reviewer Comments:
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? No
  8.7. If negative findings, was a power calculation reported to address type 2 error? No
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes