Bethany A. Bell

Making treatment effect inferences from multiple-baseline data: The utility of multilevel modeling approaches

Multiple-baseline studies are prevalent in behavioral research, but questions remain about how to best analyze the resulting data. Monte Carlo methods were used to examine the utility of multilevel models for multiplebaseline data under conditions that varied in the number of participants, number of repeated observations per participant, variance in baseline levels, variance in treatment effects, and amount of autocorrelation in the Level 1 errors. Interval estimates of the average treatment effect were examined for two specifications of the Level 1 error structure (σ2I and first-order autoregressive) and for five different methods of estimating the degrees of freedom (containment, residual, between—within, Satterthwaite, and Kenward—Roger). When the Satterthwaite or Kenward—Roger method was used and an autoregressive Level 1 error structure was specified, the interval estimates of the average treatment effect were relatively accurate. Conversely, the interval estimates of the treatment effect variance were inaccurate, and the corresponding point estimates were biased.

Access to Healthful Foods among an Urban Food Insecure Population: Perceptions versus Reality

The influence of local food environments on the risk for obesity is important overall, but may be particularly important for food insecure populations in urban settings. Access to healthful foods is most limited among racial and ethnic minorities and low-income populations; these same populations experience the highest rates of obesity and food insecurity. Few valid and reliable measures have been developed to assess the quality of local food environments. This research addresses this gap by introducing an inventory for measuring self-reported perceptions of food access and then compares the perceptions measure to objective assessments of local food environments. Data are focused on an urban population experiencing disproportionate rates of food insecurity. The four-item perceptions of food access inventory had high internal consistency (Cronbach’s alpha = 0.80). Participants’ perceptions of access to healthful foods mirrored the reality of their food environment; however, perceptions of access to alcohol and tobacco were less accurate. Findings suggest that people living in low-income, urban, minority, and food insecure communities can validly assess (in)access to healthful foods. Future research is needed to further validate the perceptions of food access measure introduced and, more importantly, to develop strategies for increasing access to healthful foods in food insecure contexts.

The Veggie Project: A Case Study of a Multi-component Farmers’ Market Intervention

This case study provides an in-depth examination of process and feasibility factors associated with the development of a multi-component environmental intervention designed to increase access to fresh fruits and vegetables in four low-income, minority, urban communities with few healthy food retail outlets. The intervention, the Veggie Project, included three components: (a) onsite farmers’ markets, (b) a Super Shopper voucher program, and (c) a Youth Leader Board. We analyzed receipts from sales transactions at the farmers’ markets, close-ended surveys with participants, in-depth interviews with project stakeholders, and journal entries completed by youth participants. Thirty-four farmers’ markets occurred, resulting in 1,101 sales transactions. Financial vouchers were used to purchased 63% of the produce. All of the youth Super Shoppers came to the market at least once and made significantly more purchase transactions than adults. The farmers’ markets were never accessed by 38% of the adult Super Shoppers. The Veggie Project increased access to healthy foods, particularly among youth. More research is warranted to examine the relationship between market use and dietary behaviors as well as other factors (i.e., besides physical and economic) influencing food access among adults.

The Guinea Pig Syndrome: Improving Clinical Trial Participation among Thoracic Patients

Background: The purpose of the study was to examine lung cancer patients’ knowledge, attitudes, and behavior regarding clinical trials and to develop an effective intervention for increasing patient knowledge and awareness of clinical trials for lung cancer patients. Methods: Qualitative semistructured, in-depth interviews were conducted with (1)new patients who had not yet interacted with their physicians, (2) existing patients who had participated in a clinical trial, and (3) existing patients who had not been offered a trial. Findings from the interviews led to the creation of a letter that was sent to all new patients before their first appointment, explaining that offering a clinical trial at this hospital was the norm, to expect this discussion, and the option of standard treatment was always available. Results: Results showed new patients and established patients had similar perceptions of trials—the fear of being a guinea pig, offering a trial meant no hope, and misconception of purpose. Existing patients who had participated in a trial expressed positive benefits of trial participation, even if their health did not improve. A year after the letter process was initiated, accrual rates increased 18% and approximately 81% of all eligible lung cancer patients were in a trial. Conclusions: The letter, addressing patient’s preexisting fears about being offered a clinical trial, appears to show some initial success in improving clinical trial accrual.

Environmental influences on fruit and vegetable intake: results from a path analytic model.

OBJECTIVE Fruit and vegetable (F&V) intake is influenced by behavioural and environmental factors, but these have rarely been assessed simultaneously. We aimed to quantify the relative influence of supermarket availability, perceptions of the food environment and shopping behaviour on F&V intake. DESIGN A cross-sectional study. SETTING Eight counties in South Carolina, USA, with verified locations of all supermarkets. SUBJECTS A telephone survey of 831 household food shoppers ascertained F&V intake with a seventeen-item screener, primary food store location, shopping frequency and perceptions of healthy food availability, and supermarket availability was calculated with a geographic information system. Path analysis was conducted. We report standardized beta coefficients on paths significant at the 0·05 level. RESULTS Frequency of grocery shopping at primary food store (β = 0·11) was the only factor exerting an independent, statistically significant direct effect on F&V intake. Supermarket availability was significantly associated with distance to utilized food store (β = -0·24) and shopping frequency (β = 0·10). Increased supermarket availability was significantly and positively related to perceived healthy food availability in the neighbourhood (β = 0·18) and ease of shopping access (β = 0·09). Collectively considering all model paths linked to perceived availability of healthy foods, this measure was the only other factor to have a significant total effect on F&V intake. CONCLUSIONS While the majority of the literature to date has suggested an independent and important role of supermarket availability for F&V intake, our study found only indirect effects of supermarket availability and suggests that food shopping frequency and perceptions of healthy food availability are two integral components of a network of influences on F&V intake.

Use of Design Effects and Sample Weights in Complex Health Survey Data: A Review of Published Articles Using Data From 3 Commonly Used Adolescent Health Surveys

OBJECTIVES We assessed how frequently researchers reported the use of statistical techniques that take into account the complex sampling structure of survey data and sample weights in published peer-reviewed articles using data from 3 commonly used adolescent health surveys. METHODS We performed a systematic review of 1003 published empirical research articles from 1995 to 2010 that used data from the National Longitudinal Study of Adolescent Health (n=765), Monitoring the Future (n=146), or Youth Risk Behavior Surveillance System (n=92) indexed in ERIC, PsycINFO, PubMed, and Web of Science. RESULTS Across the data sources, 60% of articles reported accounting for design effects and 61% reported using sample weights. However, the frequency and clarity of reporting varied across databases, publication year, author affiliation with the data, and journal. CONCLUSIONS Given the statistical bias that occurs when design effects of complex data are not incorporated or sample weights are omitted, this study calls for improvement in the dissemination of research findings based on complex sample data. Authors, editors, and reviewers need to work together to improve the transparency of published findings using complex sample data.

Do people really know what food retailers exist in their neighborhood? Examining GIS-based and perceived presence of retail food outlets in an eight-county region of South Carolina.

Measures of neighborhood food environments have been linked to diet and obesity. However, the appropriate measurement methods and how people actually perceive their food environments are still unclear. In a cross-sectional study of 939 adults, the perceived presence of food outlets was compared to the geographic-based presence of outlets within a participants neighborhood, utilizing percent agreement and Kappa statistics. Perceived presence was based on survey-administered questions, and geographic-based presence was characterized using 1-, 2-, 3- and 5-mile (1-mile=1.6km) Euclidean- and network-based buffers centered on each participants residence. Analyses were also stratified by urban and non-urban designations. Overall, an individuals perceived neighborhood food environment was moderately correlated with the geographic-based presence of outlets. The performance of an individuals perception was most optimal using a 2- or 3-mile geographic-based neighborhood boundary and/or when the participant lived in a non-urban neighborhood. This study has implications for how researchers measure the food environment.

Test-retest reliability of a questionnaire measuring perceptions of neighborhood food environment.

There is a lack of validated and reliable instruments on perception of the food environment, in particular for rural environments. We estimated the test-retest reliability of a questionnaire assessing perceptions of the food environment. A total of 101 primary food shoppers in South Carolina were interviewed by phone to assess their perceptions of the food environment and presence of different food outlet types in their neighborhood. The survey was repeated approximately one month after the initial administration. The intra-class correlation (ICC) and Phi coefficient are reported as measures of reliability. The majority of questions on perceptions of the neighborhood food environment appear highly reliable (ICCs range from 0.55 to 0.71), including the 3-item scale on healthy food availability (ICC 0.71). Compared to participants in rural areas, those in urban areas demonstrated better reliability for questions on opportunities to purchase fast food and perceived presence of a supercenter. More research is needed to evaluate potential rural-urban differences in reliability.

Neighborhood fast food availability and fast food consumption

Recent nutritional and public health research has focused on how the availability of various types of food in a persons immediate area or neighborhood influences his or her food choices and eating habits. It has been theorized that people living in areas with a wealth of unhealthy fast-food options may show higher levels of fast-food consumption, a factor that often coincides with being overweight or obese. However, measuring food availability in a particular area is difficult to achieve consistently: there may be differences in the strict physical locations of food options as compared to how individuals perceive their personal food availability, and various studies may use either one or both of these measures. The aim of this study was to evaluate the association between weekly fast-food consumption and both a persons perceived availability of fast-food and an objective measure of fast-food presence - Geographic Information Systems (GIS) - within that persons neighborhood. A randomly selected population-based sample of eight counties in South Carolina was used to conduct a cross-sectional telephone survey assessing self-report fast-food consumption and perceived availability of fast food. GIS was used to determine the actual number of fast-food outlets within each participants neighborhood. Using multinomial logistic regression analyses, we found that neither perceived availability nor GIS-based presence of fast-food was significantly associated with weekly fast-food consumption. Our findings indicate that availability might not be the dominant factor influencing fast-food consumption. We recommend using subjective availability measures and considering individual characteristics that could influence both perceived availability of fast food and its impact on fast-food consumption. If replicated, our findings suggest that interventions aimed at reducing fast-food consumption by limiting neighborhood fast-food availability might not be completely effective.

The Eating Identity Type Inventory (EITI). Development and associations with diet

People with healthy eating identities report healthier diets and demonstrate greater receptivity to nutrition interventions, but other types of eating identity are likely important. We developed the Eating Identity Type Inventory (EITI) to assess affinity with four eating identity types; healthy, meat, picky, and emotional. This study assessed factorial validity, using confirmatory factor analysis (CFA) and established reliability and convergent validity of the EITI. In a telephone survey, 968 primary household food shoppers completed the EITI and a dietary questionnaire; 101 repeated the EITI approximately 1month later.CFA revealed that an 11-item model provided acceptable fit (χ(2)=206; df=38), CFI=.938, NNFI=.925, RMSEA=.070; SRMR=.059). The EITI demonstrated acceptable internal consistencies with Cronbach alphas ranging from .61 to .82 and good test-retest reliability for healthy, emotional, and picky types (Pearsons correlations ranging from .78 to .84). Ordinary Least Squares (OLS) used to assess relationships between eating identity type and diet analyses demonstrated significant hypothesized relationships between healthy eating identity and healthier dietary intake and meat and picky eating identities and less healthy dietary intake. The EITI could facilitate behavioral and cognitive research to yield important insights for ways to more effectively design messages, interventions, and policies to promote healthy dietary behaviors.