Data for these analyses are from baseline surveys and contextual data from the Food in Our Neighborhood Study (FIONS). FIONS is a 5-year quasi-experimental natural experiment conducted in two urban, low-income, and minority communities – one in Philadelphia, PA and one in Trenton, NJ – both designated as “low access to supermarket” areas by USDA’s 2015 Food Environment Atlas [9]. Neighborhood study areas were matched on socio-demographic characteristics and each comprised a contiguous three square mile area. Cross-sectional baseline data were collected in 2017, prior to the construction and opening of a new full-service supermarket in the Philadelphia study community in early 2018 [10]. The study protocol was approved by the Institutional Review Board of University of Delaware.
Sample and Data Collection Procedures
A random sample of 2,439 addresses (n = 1,264 in Philadelphia; n = 1,175 in Trenton) was selected from a Computerized Delivery Sequence File database of residential addresses serviced by the U.S. Postal Service and purchased from Marketing Systems Group, an address based vendor [11]. A sample of approximately 1,200 randomly sampled addresses was established in each study area in order to ensure a final sample of at least 600 participants after attrition, a figure that would power the study to compare and detect changes in dietary outcomes over time.
From the random sample of addresses, participants were recruited using door-to-door (84%) and telephone (16%) methods by trained interviewers. To be eligible for the study, participants had to be 18 years of age or older, speak English or Spanish, be the primary food shopper for the household, and live within one of the study areas. After vacancies, non-responses, ineligibles, and refusals, we enrolled a sample of 796 primary household food shoppers from January through December 2017 (Fig. 1).
Figure 1. Selection Process for the Food In Our Neighborhood (FIONS) Study Sample
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Participant Surveys (shopping preferences, grocery spending, home food availability, perceived nutrition environment, and dietary outcomes data)
Study participants responded to a 65-question survey comprised of ten domains. Table 1 outlines survey domains, sources, alignment with previous tests of conceptual models [8, 12], and example survey questions. Survey questions were principally sourced from previously validated surveys [8, 13, 14]. In a few cases, as noted, the research team developed questions based on previously validated surveys. For in-home interviews, heights and weights were measured using procedures from the National Health and Nutrition Examination Survey (NHANES) [15]. For interviews conducted by phone, self-reported heights and weights were recorded.
The tenth survey domain was a 24-hour dietary recall using the Automated Self-Administered 24-Hour (ASA24®) Dietary Assessment Tool [16]. As indicated by ASA24® protocol and to reduce bias in dietary assessment, a second 24-hour dietary recall was completed (by phone) two weeks after the first data collection. SAS code from the National Institutes of Health was used to calculate dietary outcome measures from ASA24® dietary assessment data [17]. Dietary outcomes data analyzed were healthy eating index (HEI) score, fruit consumption subscore, and vegetable consumption subscore from participant ASA24® dietary assessments.
Table 1
Participant Survey Domains, Sources, and Alignment with Conceptual Models of the Nutrition Environment
Survey Domain | Number of Questions (Items) | Sources | Conceptual Model Alignment [8, 12] | Example Questions / Details |
1. Main store preferences and perceptions | 10 (29 items) | Green and Glanz [8]; Dubowitz et al. [13] | Shopping Behaviors; Perceived Consumer Nutrition Environment | What is the name and address of the main store where you most often do your major food shopping?; How do you usually get to this store?; At [main food store], how hard or easy is it to get [list of food/beverage items]? |
2. Grocery spending and household food security | 12 | 8 spending patterns questions developed based on Dubowitz et al. [13]; 2 food insecurity items from Hager et al. [14] | N/A | How much do you spend per month on groceries? How many people does this amount feed? I worried whether our food would run out before we got money to buy more (often true; sometimes true; never true) |
3. Perceptions of neighborhood food availability | 1 (6 items) | Green and Glanz [8] | Perceived Community Nutrition Environment | It is easy to buy fruits and vegetables in my neighborhood (strongly disagree to strongly agree) |
4. Home food availability | 4 (31 items) | Green and Glanz [8] | Home Food Environment | Indicate whether each of these food items were available in your home in the past week |
5. Neighborhood satisfaction and safety | 4 | Dubowitz et al. [13] | Neighborhood | I am satisfied with my neighborhood as a place to live (strongly disagree to strongly agree) |
6. Demographics | 17 | Dubowitz et al. [13] | Background Characteristics | Household income & size; race/ethnicity; gender; employment status; vehicle access |
7. Participation in food assistance (SNAP & WIC) | 6 | Dubowitz et al. [13]; 2 WIC questions developed | Background Characteristics | Did any member of your household receive [SNAP / WIC] benefits in the last year? |
8. Health status | 9 (15 items) | Green and Glanz [8]; Dubowitz et al. [13] | Background Characteristics | Have you ever been told by a doctor that you have any of the following conditions? [list]; Tobacco/alcohol use; level of physical activity |
9. Height and weight | 2 | NHANES procedures [15] | Weight | Self-reported if surveys conducted by phone |
10. 24-hour dietary recall | ASA24® tool | ASA24® Dietary Assessment Tool [16] | Eating Behaviors | ASA24® (administered twice, 2 weeks apart) for dietary outcomes data (HEI score, fruit subscore, and vegetable subscore [17] |
The majority of survey items in analyses were ordinal level variables asked on either a four-point or five-point scale. Examples of four-point Likert items were not at all important to very important while others were scaled never/rarely to almost always. All five-point scaled items were on a scale of strongly disagree to strongly agree. Continuous variables (e.g., age, distance from home to main store, grocery spending, and fruit and vegetable spending) were converted to ordinal variables for easier interpretation and to maintain consistency in item type across factor analysis. Cut points for categories were determined in ways that optimized even distribution of responses across categories.
● Store Audits (observed nutrition environment data)
This study also collected data on observed nutrition environments in supermarkets and corner stores from both study neighborhoods using Nutrition Environment Measures Survey (NEMS) tools. NEMS assessments were conducted in a total of 29 supermarkets and 31 corner stores using NEMS-S and NEMS-CS tools, respectively [18, 19]. Both types of retail outlets were scored on availability, price, and quality of both healthier and less-healthy food items.
Audits were conducted at all supermarkets in a two-mile buffer around both study areas as well as in a random sample of corner stores within both three-square-mile study areas. A master store list was compiled in 2016 from Nielsen trade data and publicly available lists of SNAP retailers [20]. Supermarkets were eligible if they were conventional, chain-operated supermarkets, not supercenters or warehouses, had at least two checkout areas and were within the two-mile buffer around the study areas. Twenty NEMS-S assessments were completed in Philadelphia, out of 21 eligible supermarkets (95%; 1 refusal), while nine NEMS-S assessments were completed in Trenton, out of 11 eligible supermarkets (82%; 1 refusal, 1 missing data).
Corner stores were eligible if they were chain or independent convenience stores, or superettes, located within the study areas. Pharmacies (e.g., RiteAid, CVS) and dollar stores (e.g., Dollar General) were excluded. Among eligible corner stores, a random sample of 22 locations was selected per study area. NEMS-CS assessments were completed in 18 of the 22 corner stores in Philadelphia out of 87 eligible (21%; 4 refusals), while NEMS-CS assessments were completed at 13 of the 22 corner stores in Trenton out of 38 eligible (34%; 9 refusals).
In order to analyze observed nutrition environment scores for individual respondents, and not only for each study area, geospatial and Bayesian statistical methods were used. This resulted in calculation of an estimated NEMS score for each study participant address, based on measured NEMS scores. For chain stores where a NEMS score was calculated for at least one location, we assigned the same or average score to other stores in the same chain. Other stores were assigned the average observed NEMS score for that class of store—i.e., supermarket, WIC-authorized corner store, or corner store not authorized by WIC. We then interpolated a raster surface using the Empirical Bayesian Kriging option in ArcGIS 10.6 Geostatistical Analyst [21] to estimate a NEMS value for each individual participant address. Kriging is a geostatistics method often applied in environmental and earth sciences to predict unknown values based on spatial patterns in sampled data [22]. Estimated NEMS scores were assigned to each participant address using the Extract Values to Points tool in ArcGIS 10.6 Spatial Analyst [21]. NEMS scores ranged from 8.3 to 23.9 (mean = 15.6; SD = 3.4).
Statistical Analyses
Analyses were conducted in two stages: exploratory factor analysis (EFA) and use of a Multiple Indicator Multiple Causes (MIMIC) model.
● Exploratory Factor Analysis (EFA)
In the first stage, an exploratory factor analysis (EFA) was conducted to identify a viable factor structure among over 120 items from participant surveys. We employed EFA over confirmatory factor analysis (CFA) to allow items to load freely onto factors. Utilization of EFA allowed data to define factors based solely on empirical correlations between items. Mplus version 8.323 with default Geomin rotation was used to allow for correlated factor structures. Exploratory factor analyses were repeated until the following criteria were met: 1) items had factor loadings greater than or equal to .40; and, 2) items had secondary factor loadings greater than or equal to .30. Items that did not meet these criteria were removed one item at a time.
EFA yielded four factors comprised of 22 indicator items. Table 2 shows the four factors, their factor loadings, and corresponding item names that were retained based on goodness of fit statistics. We interpreted factors by examining item content and patterns of coefficients. Items loading onto My Store’s Quality (Factor 1) include store cleanliness, availability of fresh foods, and store healthy programs. Items loading onto Perceptions of Neighborhood Food Availability (Factor 2) include quality, selection and ease of buying healthy foods in the community. Items loading onto Neighborhood Safety (Factor 3) characterize neighborhood satisfaction, walkability and violence. Items loading onto Household Food Challenges (Factor 4) reflect availability of unhealthy items in the home, lower grocery and fresh fruit and vegetable expenditures, and transportation barriers.
Table 2
Factors, Items and Factor Loadings Identified in Exploratory Factor Analysis of FIONS Participant Surveya
Factor and Item Descriptions | Factor Loadings |
FACTOR 1: My Store’s Quality (8 items) |
Store Cleanliness Score | 0.727 |
Store Availability of Fresh Meats Score | 0.713 |
Store Availability of Fresh Fruits and Vegetables Score | 0.682 |
Store Staff Friendliness Score | 0.605 |
Store Prices Score | 0.557 |
Store Signs to Encourage Healthy Foods Score | 0.552 |
Store Programs to Help Me Buy Healthy Foods Score | 0.443 |
Store Difficulty Getting Lean Meats Score | -0.433 |
FACTOR 2: Perceptions of Neighborhood Food Availability (6 items) |
Low-fat Products in My Neighborhood are High Quality | 0.901 |
Large Selection of Fruits and Vegetables in My Neighborhood | 0.895 |
Large Selection of Low-fat Products in My Neighborhood | 0.892 |
Easy to Buy Fruits and Vegetables in My Neighborhood | 0.871 |
Easy to Buy Low-fat Products in My Neighborhood | 0.867 |
Fruits and Vegetables in My Neighborhood are High Quality | 0.865 |
FACTOR 3: Neighborhood Safety (4 items) |
I Feel Safe Walking in My Neighborhood During the Evening | 0.810 |
I Am Satisfied With My Neighborhood as a Place to Live | 0.703 |
Violence is a Problem in My Neighborhood | -0.659 |
I Often Walk Places in My Neighborhood | 0.466 |
FACTOR 4 Household Food Challenges (4 items) |
Amount Spent per Month on Fruits and Vegetables (per person; categorical) | -0.712 |
Amount Spent per Month on Groceries (per person; categorical) | -0.634 |
Home Availability of Unhealthy Food and Beverage Items Score | 0.422 |
Does Not Drive Own Vehicle to Main Food Store | 0.408 |
a Selection criteria: primary factor loadings ≥ ± 0.40. |
● Multiple indicator multiple causes (MIMIC) Model
In the second stage of analyses, we extended EFA findings to explore relationships between latent factors and covariates using a Multiple Indicator Multiple Causes (MIMIC) model. The MIMIC model allows for simultaneous evaluation of correlations between multiple
latent factors and covariates.24 Moreover, the MIMIC model allowed us to estimate effects of latent factors on dietary outcome measures (i.e., HEI score, fruit consumption subscore, and vegetable consumption subscore,). The MIMIC model process followed required steps:24 1) confirming fit of the model using CFA on the 22 items that emerged from EFA; 2) adding covariates to the model to examine their effects on latent factors; and, 3) developing regression models between each latent factor and dietary outcomes (HEI score, fruit consumption subscore, vegetable consumption subscore), while controlling for significant covariates.
In final analyses, regression models were developed to examine the extent to which the four latent factors were related to dietary outcomes (HEI score, fruit consumption subscore, and vegetable consumption subscore), while controlling for 11 covariates that remained independently and significantly correlated with latent factors: age, gender, Black/African-American race, Hispanic ethnicity, general health status, physical activity, smoking status, alcoholic drinks per month, SNAP or WIC participation, household income category, and household size. (Education level and household food insecurity dropped from the model.)