Quantifying geocode location error using GIS methods

BACKGROUND: The Metropolitan Atlanta Congenital Defects Program (MACDP) collects maternal address information at the time of delivery for infants and fetuses with birth defects. These addresses have been geocoded by two independent agencies: (1) the Georgia Division of Public Health Office of Health Information and Policy (OHIP) and (2) a commercial vendor. Geographic information system (GIS) methods were used to quantify uncertainty in the two sets of geocodes using orthoimagery and tax parcel datasets. METHODS: We sampled 599 infants and fetuses with birth defects delivered during 1994–2002 with maternal residence in either Fulton or Gwinnett County. Tax parcel datasets were obtained from the tax assessor's offices of Fulton and Gwinnett County. High-resolution orthoimagery for these counties was acquired from the U.S. Geological Survey. For each of the 599 addresses we attempted to locate the tax parcel corresponding to the maternal address. If the tax parcel was identified the distance and the angle between the geocode and the residence were calculated. We used simulated data to characterize the impact of geocode location error. In each county 5,000 geocodes were generated and assigned their corresponding Census 2000 tract. Each geocode was then displaced at a random angle by a random distance drawn from the distribution of observed geocode location errors. The census tract of the displaced geocode was determined. We repeated this process 5,000 times and report the percentage of geocodes that resolved into incorrect census tracts. RESULTS: Median location error was less than 100 meters for both OHIP and commercial vendor geocodes; the distribution of angles appeared uniform. Median location error was approximately 35% larger in Gwinnett (a suburban county) relative to Fulton (a county with urban and suburban areas). Location error occasionally caused the simulated geocodes to be displaced into incorrect census tracts; the median percentage of geocodes resolving into incorrect census tracts ranged between 4.5% and 5.3%, depending upon the county and geocoding agency. CONCLUSION: Geocode location uncertainty can be estimated using tax parcel databases in a GIS. This approach is a viable alternative to global positioning system field validation of geocodes

Comparing perception-based and geographic information systems (GIS) based characterizations of the local food environment

Measuring features of the local food environment has been a major challenge in studying the effect of the environment on diet. This study examined associations between alternate ways of characterizing the local food environment by comparing Geographic Information System (GIS)-derived densities of various types of stores to perception-based measures of the availability of healthy foods. Survey questions rating the availability of produce and low-fat products in neighborhoods were aggregated into a healthy food availability score for 5,774 residents of North Carolina, Maryland, and New York. Densities of supermarkets and smaller stores per square mile were computed for 1 mile around each respondent’s residence using kernel estimation. The number of different store types in the area was used to measure variety in the food environment. Linear regression was used to examine associations of store densities and variety with reported availability. Respondents living in areas with lower densities of supermarkets rated the selection and availability of produce and low-fat foods 17% lower than those in areas with the highest densities of supermarkets (95% CL, −18.8, −15.1). In areas without supermarkets, low densities of smaller stores and less store variety were associated with worse perceived availability of healthy foods only in North Carolina (8.8% lower availability, 95% CL, −13.8, −3.4 for lowest vs. highest small-store density; 10.5% lower 95% CL, −16.0, −4.7 for least vs. most store variety). In contrast, higher smaller store densities and more variety were associated with worse perceived healthy food availability in Maryland. Perception- and GIS-based characterizations of the environment are associated but are not identical. Combinations of different types of measures may yield more valid measures of the environment.http://deepblue.lib.umich.edu/bitstream/2027.42/58001/1/Comparing perception based and geographic informatin systems GIS based characterizations of the local food environment.pd

The Correlates of Leisure Time Physical Activity among an Adults Population from Southern Taiwan

<p>Abstract</p> <p>Background</p> <p>Assessing the correlates of practicing physical activity during leisure time is important with regard to planning and designing public health strategies to increase beneficial behaviors among adult populations. Although the importance of leisure time physical activity (LTPA) is highlighted in many Western countries, there are not many publications on physical activity patterns, and even less on their correlates, in non-Western societies. The goal of this study was thus to explore the determinants influencing adults' leisure time physical activity (LTPA) in a city in southern Taiwan.</p> <p>Methods</p> <p>A cross-sectional population-based study was conducted in 2007, using a standardized questionnaire. Energy expenditure was dichotomized into two groups based on the recommended levels of moderate physical activity from LTPA: ≥10 or < 10 MET·hr·wk^-1. Logistic regression analyses were applied to the results.</p> <p>Results</p> <p>A total of 762 subjects with valid data took part in the study (mean age 53.8 ± 13.8 years). In multivariate logistic regression analysis, we found the following results: Age was positively associated with LTPA. Adults with stronger perceived convenience of exercise facilities (OR = 2.04; 95%CI = 1.28-3.24) and past exercise experience in school (OR = 1.86; 95%CI= 1.19-2.91) participated in more LTPA. Subjects with more general social support (OR = 1.66;95%CI = 1.13-2.44), greater knowledge about the health benefits of exercise (OR = 1.85;95%CI = 1.25-2.74), more sports media consumption (OR = 1.94;95%CI = 1.26-2.98), and higher self-efficacy (OR = 3.99;95%CI = 2.67-5.97) were more likely to engage in LTPA. Further analysis comparing different sources of social support showed only social support from friends had a significant positive association (OR = 1.73;95%CI = 1.14-2.63) with increased LTPA.</p> <p>Conclusions</p> <p>LTPA in southern city of Taiwan showed some unique associations with age, socioeconomic status and media consumption that are not commonly reported in the Western World and similar associations with regards to psychosocial correlates of LTPA participation. Further studies from developing countries are warranted to highlight culture-specific differences in physical activity participation.</p

Contribution of Individual and Environmental Factors to Physical Activity Level among Spanish Adults

BACKGROUND: Lack of physical activity (PA) is a major risk for chronic disease and obesity. The main aims of the present study were to identify individual and environmental factors independently associated with PA and examine the relative contribution of these factors to PA level in Spanish adults. METHODOLOGY/PRINCIPAL FINDINGS: A population-based cross-sectional sample of 3,000 adults (18-75 years old) from Gran Canaria (Spain) was selected using a multistage stratified random sampling method. The participants were interviewed at home using a validated questionnaire to assess PA as well as individual and environmental factors. The data were analyzed using bivariate and multivariate logistic regression. One demographic variable (education), two cognitive (self-efficacy and perceived barriers), and one social environmental (organized format) were independently associated with PA in both genders. Odds ratios ranged between 1.76-2.07 in men and 1.35-2.50 in women (both p<0.05). Individual and environmental factors explained about one-third of the variance in PA level. CONCLUSIONS/SIGNIFICANCE: Self-efficacy and perceived barriers were the most significant factors to meet an adequate level of PA. The risk of insufficient PA was twofold greater in men with primary or lesser studies and who are employed. In women, living in rural environments increased the risk of insufficient PA. The promotion of organized PA may be an efficient way to increase the level of PA in the general population. Improvement in the access to sport facilities and places for PA is a prerequisite that may be insufficient and should be combined with strategies to improve self-efficacy and overcome perceived barriers in adulthood

Fatores associados a atividade fisica, comportamento sedentario e participacao na Educacao Fisica em estudantes do Ensino Medio em Santa Catarina, Brasil

Abstract published in English and Portuguese English title: Factors associated with physical activity, sedentary behavior, and participation in physical education among high school students in Santa Catarina State, BrazilThe objectives of this study were to estimate the prevalence of insufficient physical activity, sedentary behavior, and absence from physical education and associated factors. The Santa Catarina State Adolescents' Questionnaire (COMPAC, in Portuguese) was applied to a sample of 5,028 adolescents (15-19 years of age) attending public high schools in the State of Santa Catarina, Brazil. Information included demographic and socioeconomic indicators. Poisson regression analyses were used to test associations. The proportion of students with insufficient physical activity was 28.5%, associated with low consumption of fruits and vegetables (PR = 1.27; 95%CI: 1.15; 1.40) and enrollment in night classes (PR = 1.44; 95%CI: 1.34; 1.54). Absence from physical education was reported by 48.6%; employment and older age were negatively associated with absence from physical education. Sedentary behavior was reported by 38.4%, but was less frequent in rural areas (PR = 0.52; 95%CI: 0.31; 0.83) and among those enrolled in absence from physical education (RP = 0.73; 95%CI: 0.56; 0.95). The results suggest interventions with specific strategies aimed at ameliorating each contributing factor. = O objetivo deste estudo foi analisar as prevalências e fatores associados à atividade física insuficiente, comportamento sedentário e ausência nas aulas de Educação Física em escolares do Ensino Médio. O questionário COMPAC (Comportamento do Adolescente Catarinense) foi respondido por 5.028 estudantes (15 a 19 anos), de escolas públicas de Santa Catarina, Sul do Brasil. Foram analisados comportamentos de risco, informações demográficas e sócio-econômicas. Utilizou-se regressão de Poisson para análises das associações. A prevalência de atividade física insuficiente foi de 28,5% e associou-se a um menor consumo de frutas/verduras (RP = 1,27; IC95%: 1,15-1,40) e estudo noturno (RP = 1,44; IC95%: 1,34-1,54). A prevalência de ausência nas aulas de Educação Física foi de 48,6% e associou-se negativamente à idade e com estar trabalhando (RP = 1,52; IC95%: 1,18-2,19). A prevalência de comportamento sedentário foi de 38,4%, atingindo menos os residentes de áreas rurais (RP = 0,52; IC95%: 0,31-0,83) e que participavam de uma ausência nas aulas de Educação Física semanal (RP = 0,73; IC95%: 0,56-0,95). Os resultados sugerem intervenções com estratégias específicas para cada comportamento analisado.Kelly Samara da Silva, Markus Vinícius Nahas, Karen Glazer Peres, Adair da Silva Lope