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Health Disparities

HD: Food Security (2011)

Citation:

Zenk, SN, Schultz, AJ, Israel, BA, James, SA, Bao, S, Wilson, ML. Neighborhood racial composition, neighborhood poverty and the spatial accessibility of supermarkets in metropolitan Detroit. American Journal of Public Health 2005; 95 (4): 660-667.

PubMed ID: 15798127
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To determine whether supermarkets are located at farther distances from the center of African American neighborhoods compared with White neighborhoods regardless of neighborhood economic conditions or if racial disparities in supermarket accessibility occur only in higher poverty contexts.

Inclusion Criteria:

Neighborhoods in the tri-county Detroit metropolitan area within a 10-mile buffer of Detroit.

Exclusion Criteria:

Residents outside of the defined tri-county Detroit metropolitan area.

Description of Study Protocol:

Sampling

Neighborhoods in the Detroit metropolitan area

Design

Evaluation of the spatial accessibility of supermarkets in relation to neighborhood racial composition and poverty was evaluated using 2000 decennial census data to characterize the neighborhoods and population density computed as the total population per square mile. Neighborhood poverty was defined as the percentage of residents below the poverty line. Grocery stores were identified from a 2001 list of stores from the Michigan Department of Agriculture.

Statistical Analysis

  • Ordinary least squares (OLS) regression
  • Moving average spatial regression
  • Tertiles for percentage of African American residents and percentage of residents in poverty used for statistical analysis
  • Moran's I statistic to test for evidence of spatial auto correlation in residuals from ordinary least squares regression model
  • Moran's I statistic used to test residuals from spatial regression models.

 

Data Collection Summary:

Measurements

  • 2000 decennial census data used to characterize the neighborhoods
  • Population density computed as the total population per square mile
  • Racial composition defined as the percentage of non-Hispanic African American residents
  • Neighborhood poverty defined as the percentage of residents below the poverty line (median=8.21%)
  • Spatial accessibility measured as the Manhattan block distance to the nearest supermarket, calculated using a geographic information system software.

 Dependent Variables

Spatial accessibility to grocery store

Independent Variables

  • Neighborhood economic conditions
  • Neighborhood racial composition
  • Number of supermarkets
    • Defined as super centers and full line grocery stores associated with a national or regional grocery chain.

Control Variables

None

 

Description of Actual Data Sample:
  • Initial N:
    • 869 neighborhoods as characterized by census tracts in the tri-county Detroit metropolitan area
    • 160 supermarkets in defined area
  • Age: Not applicable
  • Ethnicity: Not applicable
  • Other relevant demographics: None
  • Anthropometrics: Not applicable
  • Location: Metropolitan area of Detroit, Michigan.

 

Summary of Results:

Key Findings

  • The nearest supermarket was significantly further away in neighborhoods with a high proportion of African Americans and in the most impoverished neighborhoods compared with neighborhoods with a low proportion of African Americans and the least impoverished neighborhoods respectively when adjusted for population density
  • Mean distance to the nearest supermarket was similar in the least impoverished neighborhoods across all tertiles of percentage of African American residents
  • Mean distance to nearest supermarket increased with each successive percentage poor tertile for neighborhoods with a high proportion of African Americans but remained approximately the same across all tertiles of percentage poor for predominantly white neighborhoods
  • Distance to the nearest supermarket in impoverished neighborhoods varied considerably by percentage of African Americans.
  Model One
OLS Coefficient 
 Model One
Spatial Coefficient
Model Two 
OLS b Coefficient 
Model Two
Spacial Coefficient 

African American (percent) 

1.98-62.63 (medium)

0.086 (0.068)

0.092 (0.067)

-0.042 (0.096)

-0.028 (0.097)

African American (percent)

63.11-98.43 (high)

0.273 (0.087)


P<0.01

0.295 (0.888)
 

P<0.001

-0.004 (0.316)

-0.002 (0.314)

Poor (percent)

5.03-17.20 (medium)

0.010 (0.068)

-0.021 (0.068)

-0.048 (0.098)

-0.052 (0.097)

Poor (percent)

17.23-81.96 (high)

0.777 (0.092)

P<0.001

0.703 (0.092)

P<0.001

0.050 (0.238) -0.190 (0.239)
Medium African American x medium poverty     0.115 (0.140) 0.078 (0.140)
Medium African American x high poverty     0.999 (0.268)

P<0.001

1.125 (0.266)

P<0.001

High African American x medium poverty     0.365 (0.340) 0.319 (0.337)
High African American x high poverty     0.956 (0.418)

P<0.05

1.153 (0.391)

P<0.01

Adjusted R2 0.21   0.22   
Log likelihood   -2,699   -2,691
Likelihood ratio test       15.83

P<0.01

  

Author Conclusion:

The relationship between neighborhood racial composition and supermarket accessibility varied according to neighborhood poverty level in metropolitan Detroit. The distance to the nearest supermarket was similar among the least impoverished neighborhoods across the three tertiles of percentage African American. Disparities in supermarket accessibility based on race were evident among the most impoverished neighborhoods in which African Americans resided with the average supermarket 1.1 miles farther from the most impoverished African American neighborhoods as compared to the most impoverished White neighborhoods. 

Funding Source:
Not-for-profit
National Cancer Institute Cancer Education and Career Development Program
Reviewer Comments:

Criteria for identification of supermarkets excluded small grocery stores.

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) Yes
  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? Yes
  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) N/A
  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%.) N/A
  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? No
  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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? Yes
  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? Yes
  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? Yes
  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? N/A
  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? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
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