HD: Food Security (2011)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

This study describes the prevalence of places where people can obtain food in their neighborhoods. The hypothesis was tested that fewer supermarkets and more corner markets are located in low-wealth neighborhoods compared to higher-wealth neighborhoods. It was also investigated whether the prevalence of food stores and food service places is associated with the proportion of black residents. The hypothesis was tested that fewer supermarkets and more corner markets are located in predominately black neighborhoods compared to racially mixed or predominately white neighborhoods.

Inclusion Criteria:

The 221 census tracts defined in the 1990 census were used as proxies for neighborhoods in the following areas: Jackson City, Mississippi; Forsyth County, North Carolina; Washington County, Maryland; and selected suburbs of Minneapolis, Minnesota. This research is ancillary to the Atherosclerosis Risk in Communities (ARIC) study, an ongoing study of atherosclerosis based on sample populations from these areas.

Exclusion Criteria:

Census tracts with ten or fewer housing units were excluded. Of the 3987 business addresses obtained, 99.5% were geocoded to census tracts; 80 businesses were excluded because the census tract for that business did not fall within the geographic boundaries of the study areas or the census tract had been excluded. Finally, 548 duplicate records were deleted. Department stores, catering businesses and liquor stores were also excluded as places where people regularly obtain food.

Description of Study Protocol:

Recruitment

Locations were obtained from the 221 census tracts as defined in the 1990 census.

Design

Cross sectional

Blinding used

Not applicable 

Intervention

Not applicable 

Statistical Analysis

Poisson regressions were used to evaluate the relationship between the number of stores and neighborhood wealth and racial composition.

 

Data Collection Summary:

Timing of Measurements

Final census tracts were looked at in Mississippi, North Carolina, Maryland and Minnesota. Business addresses of places where people can buy food were collected from the local departments of agriculture. The 1997 North America Industry Classification System (NAICS) codes and definitions were modified to describe the types of food stores and food service places located in each census tract. Supermarkets were defined as large, corporate-owned chain stores. Grocery stores were defined as smaller non-corporate-owned food stores. Convenience stores attached to gas stations were added to the food and beverage stores subsector. All specialty food stores were grouped together. Cafeterias were grouped with full-service restaurants. Carry-out eating places sell fast but are not franchised fast-food places. Specialty carry-out eating places specialize in one type of food. 

Dependent Variables

Number of stores

Independent Variables

  • Neighborhood wealth
  • Racial composition of neighborhoods.

Control Variables

Not applicable

Description of Actual Data Sample:
  • Initial N: 221 census tracts and 3,987 businesses
  • Attrition (final N): 216 tracts and 3,341 businesses
  • Age: Not applicable
  • Ethnicity: Americans
  • Other relevant demographics: (based on neighborhood wealth shown as mean±SD)
    • Population density (persons per square Km)
      • Low (N=44) 1,456±1012
      • Low-medium (N=43) 1,335±1044
      • Medium (N=42) 895±703
      • High-medium (N=43) 588±458
      • High (N=44) 619±479
    • Percentage of residents who are renters (based on N above)
      • Low 0.46±0.20
      • Low-Medium 0.41±0.20
      • Medium 0.29±0.14
      • High-medium 0.30±0.20
      • High 0.22±0.15
    • Percentage of residents who are black American
      • Low 0.53±0.42
      • Low-Medium 0.36±0.38
      • Medium 0.18±0.29
      • High-Medium 0.13±0.21
      • High 0.06±0.14
    • Percentage of households without a vehicle
      • Low 0.19±0.24 white/0.32±0.26 black
      • Low-Medium 0.17±0.22 white/0.20±0.17 black
      • Medium 0.06±0.05 white/0.11±0.19 black
      • Medium-high 0.05±0.06 white/0.10±0.13 black
      • High 0.03±0.04 white/0.06±0.11 black
  • Anthropometrics: Not noted
  • Location: Mississippi, North Carolina, Maryland and Minnesota.

 

Summary of Results:

Key Findings

  • On average, the lower-wealth groups contain the fewest people and the areas of these tracts are the smallest. Nonetheless, the population density of the lowest wealth group is the highest.
  • As the wealth of the neighborhoods decrease, the proportion of black residents increase, with over eight times as many black Americans living in the lowest-wealth neighborhoods compared to the highest-wealth areas. Furthermore, the proportion of households without a car or truck available is also higher among black Americans regardless of wealth.
  • The types of food stores and food service places that exist in poor and wealthy neighborhoods are different; there are over three times as many supermarkets in the wealthier neighborhoods compared to the lowest-wealth areas
  • Convenience stores with gas stations are also more commonly found in wealthier areas with the medium-wealth neighborhoods having the highest prevalence of these types of establishments
  • The wealthier neighborhoods contain fewer small grocery stores, convenience stores and specialty food stores compared to the lowest-wealth neighborhoods
  • The most prevalent type of food service place is the full-service restaurant; on average three to four full-service restaurants are located in each neighborhood
  • Fast food restaurants are more prevalent in the low-medium and medium-wealth neighborhoods and become less prevalent in the highest-wealth neighborhoods
  • Carry-out specialty eating places are 50-80% more prevalent in the wealthier neighborhoods
  • As wealth increases, the number of bars and taverns decline
  • Regarding neighborhood racial segregation, supermarkets and specialty food stores are more common in racially mixed and predominately white neighborhoods
  • The greatest difference is in the prevalence of supermarkets, which are four times more common in predominately white neighborhoods compared to predominately black neighborhoods
  • Smaller grocery stores, convenience stores and convenience stores attached to gas stations are less common in predominately white neighborhoods
  • Mixed and predominately white neighborhoods are similar in the prevalence of food store types compared to predominately black neighborhoods
  • Compared to predominately black neighborhoods, all food service places are more prevalent in racially mixed and predominately white neighborhoods, except bars and taverns, which are less common in white neighborhoods
  • Full-service restaurants are two times more prevalent in white neighborhoods and three times more prevalent in racially mixed neighborhoods
  • Fast food restaurants and carryout eating places are twice as common in white and racially mixed neighborhoods
  • Carry-out eating places serving specialty items are nine to 11 times more prevalent in racially mixed and predominately white areas.
Author Conclusion:
  • This study shows that the locations of food stores and food service places are associated with the wealth and racial makeup of neighborhoods and, in the case of supermarkets and small corner grocery stores, this association is in the expected direction
  • Results of this study support previous research that suggests people's dietary choices may be influenced by the availability of food stores and food service places
  • The clustering of census tracts along lines of race, ethnicity and wealth means the local food environment can be characterized at larger spatial scales
  • The results show that fewer households in poor and black neighborhoods have access to private transportation which support findings that residents of these neighborhoods have greater difficulty obtaining healthy food.
Funding Source:
Government: National Institute of Environmental Health Sciences, grant #2 R25 ES08206-05 under the
University/Hospital: University of North Carolina School of Medicine, Women's Health Research Grant
Reviewer Comments:
  • The study did not take into account the similarity of characteristics shared by neighboring census tracts, sometimes referred to as spatial auto correction
  • Information on membership of census tracts in larger neighborhood aggregations similar to the aggregation of census block groups into tracts were not available for analysis in this article.
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? N/A
  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.) Yes
  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? 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.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? Yes
  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? 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? N/A
  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)? No
  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