[Show abstract][Hide abstract] ABSTRACT: Background:
There is evidence that rural residents experience a health disadvantage compared to urban residents, associated with a greater prevalence of health risk factors and socioeconomic differences. We examined differences between urban and rural Canadians using data from the Canadian Human Activity Pattern Survey (CHAPS) 2.
Data were collected from 1460 respondents in two rural areas (Haldimand-Norfolk, Ontario and Annapolis Valley-Kings County, Nova Scotia) and 3551 respondents in five urban areas (Vancouver, Edmonton, Toronto, Montreal, and Halifax) using a 24-h recall diary and supplementary questionnaires administered using computer-assisted telephone interviews. We evaluated differences in time-activity patterns, occupational activity, and housing characteristics between rural and urban populations using multivariable linear and logistic regression models adjusted for design as well as demographic and socioeconomic covariates. Taylor linearization method and design-adjusted Wald tests were used to test statistical significance.
After adjustment for demographic and socioeconomic covariates, rural children, adults and seniors spent on average 0.7 (p < 0.05), 1.2 (p < 0.001), and 0.9 (p < 0.001) more hours outdoors per day respectively than urban counterparts. 23.1 % (95 % CI: 19.0-27.2 %) of urban and 37.8 % (95 % CI: 31.2-44.4 %) of rural employed populations reported working outdoors and the distributions of job skill level and industry differed significantly (p < 0.001) between urban and rural residents. In particular, 11.4 % of rural residents vs. 4.9 % of urban residents were employed in unskilled jobs, and 11.5 % of rural residents vs. <0.5 % of urban residents were employ in primary industry. Rural residents were also more likely than urban residents to report spending time near gas or diesel powered equipment other than vehicles (16.9 % vs. 5.2 %, p < 0.001), more likely to report wood as a heating fuel (9.8 % vs. <0.1 %; p < 0.001 for difference in distribution of heating fuels), less likely to have an air conditioner (43.0 % vs. 57.2 %, p < 0.001), and more likely to smoke (29.1 % vs. 19.0 %, p < 0.001). Private wells were the main water source in rural areas (68.6 %) in contrast to public water systems (97.6 %) in urban areas (p < 0.001). Despite these differences, no differences in self-reported health status were observed between urban and rural residents.
We identified a number of differences between urban and rural residents, which provide evidence pertinent to the urban-rural health disparity.
Environmental Health 11/2015; 14(1):88. DOI:10.1186/s12940-015-0075-y · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Health risks associated with short-term exposure to ambient air pollution are communicated to the public by the US EPA through the Air Quality Index (AQI), but it remains unclear whether the current regulatory-based, single-pollutant AQI fully represents the actual risks of air pollution-related illness. The objective of this study is to quantify cardiovascular hospital admissions attributable to PM2.5 at each AQI category. Based on National Ambient Air Quality Standards (NAAQS), the highest AQI value among criteria pollutants (driver pollutant) is reported daily. We investigated excess cardiovascular hospital admissions attributable to fine particulate matter (PM2.5) exposure from 2000 to 2010 in Bronx, Erie, Queens, and Suffolk counties of New York. Daily total, unscheduled cardiovascular hospital admissions (principal diagnosis) for individuals aged 20-99 years, concentration-response functions for PM2.5, and estimated quarterly effective daily concentrations were used to calculate excess cardiovascular hospital admissions when PM2.5 was reported as the driver pollutant and when PM2.5 was not reported as the driver pollutant at each AQI category. A higher proportion of excess hospital admissions attributable to PM2.5 occurred when PM2.5 was the driver pollutant (i.e., ~70% in Bronx County). The majority of excess hospital admissions (i.e., >90% in Bronx County) occurred when the AQI was <100 ("good" or "moderate" level of health concern) regardless of whether PM2.5 was the driver pollutant. During the warm season (April-September), greater excess admissions in Suffolk County occurred when PM2.5 was not the AQI driver pollutant. These results indicate that a single-pollutant index may inadequately communicate the adverse health risks associated with air pollution.Journal of Exposure Science and Environmental Epidemiology advance online publication, 15 July 2015; doi:10.1038/jes.2015.43.
Journal of Exposure Science and Environmental Epidemiology 07/2015; DOI:10.1038/jes.2015.43 · 3.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Socioeconomic status (SES) is an important determinant of health and potential modifier of the effects of environmental contaminants. There has been a lack of comprehensive indices for measuring overall SES in Canada. Here, a more comprehensive SES index is developed aiming to support future studies exploring health outcomes related to environmental pollution in Canada.
SES variables (n = 22, Census Canada 2006) were selected based on: cultural identities, housing characteristics, variables identified in Canadian environmental injustice studies and a previous deprivation index (Pampalon index). Principal component analysis with a single varimax rotation (factor loadings ≥ │60│) was performed on SES variables for 52974 census dissemination areas (DA). The final index was created by averaging the factor scores per DA according to the three components retained. The index was validated by examining its association with preterm birth (gestational age < 37 weeks), term low birth weight (LBW, <2500 g), small for gestational age (SGA, <10 percentile of birth weight for gestational age) and PM2.5 (particulate matter ≤ 2.5 μm) exposures in Edmonton, Alberta (1999-2008).
Index values exhibited a relatively normal distribution (median = 0.11, mean = 0.0, SD = 0.58) across Canada. Values in Alberta tended to be higher than in Newfoundland and Labrador, Northwest Territories and Nunavut (Pearson chi-square p < 0.001 across provinces). Lower quintiles of our index and the Pampalon's index confirmed know associations with a higher prevalence of LBW, SGA, preterm birth and PM2.5 exposure. Results with our index exhibited greater statistical significance and a more consistent gradient of PM2.5 levels and prevalence of pregnancy outcomes.
Our index reflects more dimensions of SES than an earlier index and it performed superiorly in capturing gradients in prevalence of pregnancy outcomes. It can be used for future research involving environmental pollution and health in Canada.
BMC Public Health 07/2015; 15(1):714. DOI:10.1186/s12889-015-1992-y · 2.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Numerous studies have examined associations between air pollution and pregnancy outcomes but most have been restricted to urban populations living near monitors.
To examine the association between pregnancy outcomes and fine particulate matter in a large national study including urban and rural areas.
Analyses were based on approximately 3 million singleton live births in Canada between 1999 and 2008. Exposures to PM2.5 (particles of median aerodynamic diameter < 2.5 µm) were assigned by mapping the mother's postal code to a monthly surface based on a national land use regression model that incorporated observations from fixed-site monitoring stations and satellite-derived estimates of PM2.5. Generalized estimating equations were used to examine the association between PM2.5 and preterm birth (gestational age < 37 weeks), term low birth weight (<2500 g), small for gestational age (SGA, <10th percentile of birth weight for gestational age), and term birth weight, adjusting for individual covariates and neighbourhood socioeconomic status (SES).
In fully adjusted models, a 10 µg/m(3) increase in PM2.5 over the entire pregnancy was associated with SGA (OR = 1.04, 95% CI 1.01, 1.07) and reduced term birth weight (-20.5 g, 95% CI -24.7, -16.4). Associations varied across subgroups based on maternal place of birth and period (1999-2003 vs. 2004-2008).
This study based on approximately 3 million births across Canada and employing PM2.5 estimates from a national spatiotemporal model provides further evidence linking PM2.5 and pregnancy outcomes.
Environmental Health Perspectives 06/2015; DOI:10.1289/ehp.1408995 · 7.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Childhood asthma development has been associated with active maternal smoking during pregnancy, but its association with maternal second-hand smoke exposure in pregnancy needs to be evaluated.
We investigated longitudinal associations between maternal smoke exposure in pregnancy and childhood asthma development.
In a population-based cohort of 5619 seven-year-old Toronto children, parents reported age of physician-diagnosed asthma development, maternal smoking during pregnancy, home second-hand smoke exposure from pregnancy until 7 years, demographics, and family history of atopy. By using Cox proportional and discrete-time hazard survival analyses, we evaluated associations between asthma and maternal smoking or home second-hand smoke exposure in pregnancy.
During pregnancy, 5.0% of mothers smoked and 6.2% were nonsmokers and exposed to home second-hand smoke; 15.5% of children developed asthma. Children whose mothers smoked or were exposed to home second-hand smoke during pregnancy were more likely to develop asthma (adjusted hazard ratio [HR] 1.30 [95% CI, 1.06-1.60]). The association persisted for children of nonsmoking mothers with home second-hand smoke exposure during pregnancy (adjusted HR 1.34 [95% CI, 1.01-1.76]), children with asthma symptoms in the past year (adjusted HR 1.36 [95% CI, 1.03-1.79]), and after adjusting for home second-hand smoke exposure from birth to age 7 years.
Maternal home second-hand smoke exposure during pregnancy is associated with incident physician-diagnosed childhood asthma, even if the mother does not smoke actively during pregnancy. Childhood asthma prevention programs should include smoking cessation strategies targeted toward smokers who live in the homes of smoking and nonsmoking pregnant women as well as pregnant women who smoke.
[Show abstract][Hide abstract] ABSTRACT: Estimation of population exposure is a main component of human health risk assessment for environmental contaminants. Population-level exposure assessments require time-activity pattern distributions in relation to microenvironments where people spend their time. Societal trends may have influenced time-activity patterns since previous Canadian data were collected 15 years ago. The Canadian Human Activity Pattern Survey 2 (CHAPS 2) was a national survey conducted in 2010-2011 to collect time-activity information from Canadians of all ages. Five urban and two rural locations were sampled using telephone surveys. Infants and children, key groups in risk assessment activities, were over-sampled. Survey participants (n = 5,011) provided time-activity information in 24-hour recall diaries and responded to supplemental questionnaires concerning potential exposures to specific pollutants, dwelling characteristics, and socio-economic factors. Results indicated that a majority of the time was spent indoors (88.9%), most of which was indoors at home, with limited time spent outdoors (5.8%) or in a vehicle (5.3%). Season, age, gender and rurality were significant predictors of time activity patterns. Compared to earlier data, adults reported spending more time indoors at home and adolescents reported spending less time outdoors, which could be indicative of broader societal trends. These findings have potentially important implications for assessment of exposure and risk. The CHAPS 2 data also provide much larger sample sizes to allow for improved precision and are more representative of infants, children and rural residents.
International Journal of Environmental Research and Public Health 02/2014; 11(2):2108-24. DOI:10.3390/ijerph110202108 · 2.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitrogen dioxide (NO2), a surrogate measure of traffic-related air pollution (TRAP), has been associated with incident childhood asthma. Timing of exposure and atopic status may be important effect modifiers. We collected cross-sectional data on asthma outcomes from Toronto school children aged 5-9years in 2006. Lifetime home, school and daycare addresses were obtained to derive birth and cumulative NO2 exposures for a nested case-control subset of 1497 children. Presence of other allergic disease (a proxy for atopy) was defined as self-report of one or more of doctor-diagnosed rhinitis, eczema, or food allergy. Generalized estimating equations were used to adjust for potential confounders, and examine hypothesized effect modifiers while accounting for clustering by school. In children with other allergic disease, birth, cumulative and 2006 NO2 were associated with lifetime asthma (OR 1.46, 95% CI 1.08-1.98; 1.37, 95% CI 1.00-1.86; and 1.60, 95% CI 1.09-2.36 respectively per interquartile range increase) and wheeze (OR 1.44, 95% CI 1.10-1.89; 1.31, 95% CI 1.02-1.67; and 1.60, 95% CI 1.16-2.21). No or weaker effects were seen in those without allergic disease, and effect modification was amplified when a more restrictive algorithm was used to define other allergic disease (at least 2 of doctor diagnosed allergic rhinitis, eczema or food allergy). The effects of modest NO2 levels on childhood asthma were modified by the presence of other allergic disease, suggesting a probable role for allergic sensitization in the pathogenesis of TRAP initiated asthma.
Environment international 01/2014; 65C:83-92. DOI:10.1016/j.envint.2014.01.002 · 5.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Air Quality Health Index (AQHI) is an aggregate measure of outdoor air quality. We investigated associations between the AQHI and emergency department (ED) visits for acute ischemic stroke to validate the AQHI as a predictor of risk of morbidity from stroke. ED visits in Edmonton, Canada between 1998 and 2002 were linked to hourly AQHI values and concentrations of carbon monoxide (CO), nitrogen dioxide (NO2), ozone, particulate matter with aerodynamic diameter less than 2.5 and 10 μm, and sulfur dioxide. A time-stratified case-crossover analysis was employed, and measures of association were adjusted for temperature and relative humidity. The AQHI, NO2 and CO were positively associated with the number of ED visits for ischemic stroke during April-September, and associations were strongest for persons 75 years of age and older. In this age range, the odds ratios (95% confidence intervals) for an interquartile range increase of AQHI in 1-24 h, 25-48 h, and 1-72 h lag periods were 1.23 (1.08-1.40), 1.15 (1.01-1.31), and 1.30 (1.10-1.54), respectively. Significant positive associations were also observed for NO2 and CO. Our finding that ED visits for stroke were significantly associated with the AQHI suggests that the AQHI may be a valid communication tool for air pollution morbidity effects related to stroke.Journal of Exposure Science and Environmental Epidemiology advance online publication, 4 December 2013; doi:10.1038/jes.2013.82.
Journal of Exposure Science and Environmental Epidemiology 12/2013; 24(4). DOI:10.1038/jes.2013.82 · 3.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Persons with underlying health conditions may be at higher risk for the short-term effects of air pollution. We have extended our original mortality time series study in Montreal, Quebec, among persons 65years of age and older, for an additional 10years (1990-2003) to assess whether these associations persisted and to investigate new health conditions.
We created subgroups of subjects diagnosed with major health conditions one year before death using billing and prescription data from the Quebec Health Insurance Plan. We used parametric log-linear Poisson models within the distributed lag non-linear models framework, that were adjusted for long-term temporal trends and daily maximum temperature, for which we assessed associations with NO2, O3, CO, SO2, and particles with aerodynamic diameters 2.5μm in diameter or less (PM2.5). We found positive associations between daily non-accidental mortality and all air pollutants but O3 (e.g., for a cumulative effect over a 3-day lag, with a mean percent change (MPC) in daily mortality of 1.90% [95% confidence interval: 0.73, 3.08%] for an increase of the interquartile range (17.56μgm(-3)) of NO2). Positive associations were found amongst persons having cardiovascular disease (cumulative MPC for an increase equal to the interquartile range of NO2=2.67%), congestive heart failure (MPC=3.46%), atrial fibrillation (MPC=4.21%), diabetes (MPC=3.45%), and diabetes and cardiovascular disease (MPC=3.50%). Associations in the warm season were also found for acute and chronic coronary artery disease, hypertension, and cancer. There was no persuasive evidence to conclude that there were seasonal associations for cerebrovascular disease, acute lower respiratory disease (defined within 2months of death), airways disease, and diabetes and airways disease.
These data indicate that individuals with certain health conditions, especially those with diabetes and cardiovascular disease, hypertension, atrial fibrillation, and cancer, may be susceptible to the short-term effects of air pollution.
Science of The Total Environment 07/2013; 463-464C:931-942. DOI:10.1016/j.scitotenv.2013.06.095 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Determine if children with asthma are more/less likely to walk to school, and if the living distance modifies this association. Five thousand six hundred nineteen children aged 5–9 completed the Toronto Child Health Evaluation Questionnaire. The mode of transportation was defined as walking, driven by car, or school bus. Children were categorized by the International Study of Asthma and Allergies in Childhood methodology as doctor-diagnosed current or lifetime asthma, symptomatic controls (asthma symptoms without diagnosis), or asymptomatic controls. The living distance was the shortest driving distance between home and school. Adjusted models revealed children with current asthma [odds ratio (OR) 1.29; 95% CI 1.01–1.65], lifetime asthma (OR 1.26; 95% CI 1.01–1.56), and symptomatic controls (OR 1.34; 95% CI 1.14–1.59) were more likely to be driven by car versus asymptomatic controls. Among children who lived within walking distance of the school (≤1.5 km), symptomatic controls were more likely to be driven by car (OR 1.30, 95% CI 1.09–1.56) or school bus (OR 1.48, 95% CI 1.01–2.17); however, children with current (OR 1.71, 95% CI 1.00–2.92), or lifetime asthma (OR 1.71, 95% CI 1.06–2.76) were more likely to be driven only by school bus. Children with asthma or respiratory symptoms are less likely to walk and more likely to be driven to school. Among children who are ineligible for school bus programs based on the living distance from school, children with asthma are still more likely to be bussed.
[Show abstract][Hide abstract] ABSTRACT: Low birth weight and preterm birth have a substantial public health impact. Studies examining their association with outdoor air pollution were identified using searches of bibliographic databases and reference lists of relevant papers. Pooled estimates of effect were calculated, heterogeneity was quantified, meta-regression was conducted and publication bias was examined. Sixty-two studies met the inclusion criteria. The majority of studies reported reduced birth weight and increased odds of low birth weight in relation to exposure to carbon monoxide (CO), nitrogen dioxide (NO(2)) and particulate matter less than 10 and 2.5 microns (PM(10) and PM(2.5)). Effect estimates based on entire pregnancy exposure were generally largest. Pooled estimates of decrease in birth weight ranged from 11.4 g (95% confidence interval -6.9-29.7) per 1 ppm CO to 28.1g (11.5-44.8) per 20 ppb NO(2), and pooled odds ratios for low birth weight ranged from 1.05 (0.99-1.12) per 10 μg/m(3) PM(2.5) to 1.10 (1.05-1.15) per 20 μg/m(3) PM(10) based on entire pregnancy exposure. Fewer effect estimates were available for preterm birth and results were mixed. Pooled odds ratios based on 3rd trimester exposures were generally most precise, ranging from 1.04 (1.02-1.06) per 1 ppm CO to 1.06 (1.03-1.11) per 20 μg/m(3) PM(10). Results were less consistent for ozone and sulfur dioxide for all outcomes. Heterogeneity between studies varied widely between pollutants and outcomes, and meta-regression suggested that heterogeneity could be partially explained by methodological differences between studies. While there is a large evidence base which is indicative of associations between CO, NO(2), PM and pregnancy outcome, variation in effects by exposure period and sources of heterogeneity between studies should be further explored.
Environmental Research 06/2012; 117:100-11. DOI:10.1016/j.envres.2012.05.007 · 4.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The monetized value of avoided premature mortality typically dominates the calculated benefits of air pollution regulations; therefore, characterization of the uncertainty surrounding these estimates is key to good policymaking. Formal expert judgment elicitation methods are one means of characterizing this uncertainty. They have been applied to characterize uncertainty in the mortality concentration-response function, but have yet to be used to characterize uncertainty in the economic values placed on avoided mortality. We report the findings of a pilot expert judgment study for Health Canada designed to elicit quantitative probabilistic judgments of uncertainties in Value-per-Statistical-Life (VSL) estimates for use in an air pollution context. The two-stage elicitation addressed uncertainties in both a base case VSL for a reduction in mortality risk from traumatic accidents and in benefits transfer-related adjustments to the base case for an air quality application (e.g., adjustments for age, income, and health status). Results for each expert were integrated to develop example quantitative probabilistic uncertainty distributions for VSL that could be incorporated into air quality models.
[Show abstract][Hide abstract] ABSTRACT: Increasing evidence links air pollution to the risk of cardiovascular disease. This study investigated the association between ischemic heart disease (IHD) prevalence and exposure to traffic-related air pollution (nitrogen dioxide [NO₂], fine particulate matter [PM₂.₅], and ozone [O₃]) in a population of susceptible subjects in Toronto. Local (NO₂) exposures were modeled using land use regression based on extensive field monitoring. Regional exposures (PM₂.₅, O₃) were modeled as confounders using inverse distance weighted interpolation based on government monitoring data. The study sample consisted of 2360 patients referred during 1992 to 1999 to a pulmonary clinic at the Toronto Western Hospital in Toronto, Ontario, Canada, to diagnose or manage a respiratory complaint. IHD status was determined by clinical database linkages (ICD-9-CM 412-414). The association between IHD and air pollutants was assessed with a modified Poisson regression resulting in relative risk estimates. Confounding was controlled with individual and neighborhood-level covariates. After adjusting for multiple covariates, NO₂ was significantly associated with increased IHD risk, relative risk (RR) = 1.33 (95% confidence interval [CI]: 1.2, 1.47). Subjects living near major roads and highways had a trend toward an elevated risk of IHD, RR = 1.08 (95% CI: 0.99, 1.18). Regional PM₂.₅ and O₃ were not associated with risk of IHD.
Journal of Toxicology and Environmental Health Part A 04/2012; 75(7):402-11. DOI:10.1080/15287394.2012.670899 · 2.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Few cohort studies have evaluated the risk of mortality associated with long-term exposure to fine particulate matter [≤ 2.5 μm in aerodynamic diameter (PM(2.5))]. This is the first national-level cohort study to investigate these risks in Canada.
We investigated the association between long-term exposure to ambient PM(2.5) and cardiovascular mortality in nonimmigrant Canadian adults.
We assigned estimates of exposure to ambient PM(2.5) derived from satellite observations to a cohort of 2.1 million Canadian adults who in 1991 were among the 20% of the population mandated to provide detailed census data. We identified deaths occurring between 1991 and 2001 through record linkage. We calculated hazard ratios (HRs) and 95% confidence intervals (CIs) adjusted for available individual-level and contextual covariates using both standard Cox proportional survival models and nested, spatial random-effects survival models.
Using standard Cox models, we calculated HRs of 1.15 (95% CI: 1.13, 1.16) from nonaccidental causes and 1.31 (95% CI: 1.27, 1.35) from ischemic heart disease for each 10-μg/m(3) increase in concentrations of PM(2.5). Using spatial random-effects models controlling for the same variables, we calculated HRs of 1.10 (95% CI: 1.05, 1.15) and 1.30 (95% CI: 1.18, 1.43), respectively. We found similar associations between nonaccidental mortality and PM2.5 based on satellite-derived estimates and ground-based measurements in a subanalysis of subjects in 11 cities.
In this large national cohort of nonimmigrant Canadians, mortality was associated with long-term exposure to PM(2.5). Associations were observed with exposures to PM(2.5) at concentrations that were predominantly lower (mean, 8.7 μg/m(3); interquartile range, 6.2 μg/m(3)) than those reported previously.
Environmental Health Perspectives 02/2012; 120(5):708-14. DOI:10.1289/ehp.1104049 · 7.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Childhood asthma prevalence is widely measured by parental proxy report of physician-diagnosed asthma in questionnaires. Our objective was to validate this measure in a North American population.
The 2884 study participants were a subsample of 5619 school children aged 5 to 9 years from 231 schools participating in the Toronto Child Health Evaluation Questionnaire study in 2006. We compared agreement between "questionnaire diagnosis" and a previously validated "health claims data diagnosis". Sensitivity, specificity and kappa were calculated for the questionnaire diagnosis using the health claims diagnosis as the reference standard.
Prevalence of asthma was 15.7% by questionnaire and 21.4% by health claims data. Questionnaire diagnosis was insensitive (59.0%) but specific (95.9%) for asthma. When children with asthma-related symptoms were excluded, the sensitivity increased (83.6%), and specificity remained high (93.6%).
Our results show that parental report of asthma by questionnaire has low sensitivity but high specificity as an asthma prevalence measure. In addition, children with "asthma-related symptoms" may represent a large fraction of under-diagnosed asthma and they should be excluded from the inception cohort for risk factor studies.
BMC Pulmonary Medicine 11/2011; 11(1):52. DOI:10.1186/1471-2466-11-52 · 2.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Self-reported data on the municipality of residence were used to assess long-term exposure to outdoor air pollution from 1980 to 2002 in the longitudinal Canadian National Population Health Survey. Exposure to carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter was determined using data obtained from fixed-site air pollution monitors operated principally in urban areas. Four different methods of attributing pollution exposure were used based on residence in (1) 1980, (2) 1994, (3) 1980 and 1994, and (4) at all locations between 1980 and 2002. Between 1,693 and 4,274 of 10,515 members of the cohort could be assigned exposures to individual pollutants using these methods. On average, subjects spent 71.4% of the 1980-2002 period in the census subdivision where they lived in 1980. A single exposure measure in 1980 or 1994 or a mean of the two measures was highly correlated (r>0.7, P<0.0001) with a measure which accounted for all moves between 1980 and 2002. Although our ability to characterize long-term exposure was constrained by a lack of data from fixed-site monitors, the low frequency of moves meant that measures based on a single year generally provided a good approximation of long-term exposure at the census subdivision level.
Journal of Exposure Science and Environmental Epidemiology 07/2011; 21(4):337-42. DOI:10.1038/jes.2010.37 · 3.19 Impact Factor