Cohort studies
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Cohort Studies
For this application you are to read the following cohort study article. After reading the article, complete the Cohort Study Template is below.
•Beelen, R., Hoek, G., Van Den Brandt, P., Goldbohm, R., Fischer, P., Schouten, L., et al. (2008). Long-term effects of traffic-related air pollution on mortality in a Dutch cohort (NLCS-AIR Study). Environmental Health Perspectives, 116(2), 196-202.
Use the Academic Search Premier database, and search using the article’s Accession Number: 31169911
Cohort Study
Submitted By (make sure your name and date are included here):
Article Citation in APA format:
Research Question:
Health Outcome of Interest:
Exposure(s) of Interest:
Type of Study (please indicate whether this is a prospective (concurrent) or retrospective (non-concurrent) or ambidirectional study:
Description/Ascertainment of Cohort:
Data Collection at Baseline:
Type, Frequency and Duration of Follow-Up (indicate something about loss to follow-up and any efforts that were made to minimize loss to follow-up and include information on the characteristics of those who were lost to follow-up and comment on why this is important):
Type of Data Analysis (include measure of association used):
Results/Main Findings of Study:
Assessment of Bias (selection and information):
Assessment of Confounders:
Comments:
SAMPLE ANSWER
Cohort Studies
Article Citation: Beelen, R., Hoek, G., Van Den Brandt, P., Goldbohm, R., Fischer, P., Schouten, L., et al. (2008). Long-term effects of traffic-related air pollution on mortality in a Dutch cohort (NLCS-AIR Study). Environmental Health Perspectives, 116(2), 196-202.
Research Question: what is the association between mortality and continuing exposure to traffic-related air pollution?
Health Outcome of Interest: decreased respiratory mortality by reducing exposure to ambient air pollution
Exposure(s) of Interest: long-term exposure to traffic-related air pollution. In essence, exposure to sulfur dioxide (SO2), nitrogen dioxide (NO2), black smoke (BS), particulate matter (PM) in addition to a variety of exposure variables to traffic comprised the exposures of interest in the study which were estimated at the home address (Beelen et al., 2008).
Type of Study: this is a prospective cohort study. In essence, a prospective cohort study is understood as a study in which the effects of a given variable are plotted over time, and the research study becomes a continuing and long-term process (Gehring et al., 2006). This cohort study is prospective given that it fits the definition of prospective; it was initiated in the year 1986, and the authors assessed mortality between 1/1/1987 and 31/12/1996, meaning that it was an ongoing process.
Description/Ascertainment of Cohort: the Netherlands Cohort Study on Diet and Cancer was started with enrolling 120,852 subjects that consisted of 62,573 women and 58,279 men aged between 55 years to 69 years, who lived in 204 municipalities all through the nation (Beelen et al., 2008).
Data Collection at Baseline: Baseline questionnaire was used to collect data. At baseline, every subject filled out an 11-page questionnaire on nutritional habits, as well as other factors for cancer. For every subject, data obtained from one page of the questionnaire were entered at baseline – with information pertaining to smoking status, sex, and age.
Type, Frequency and Duration of Follow-Up: After recruitment of the subjects, all of them were followed up for cancer incidence by record linkage to registries of cancer. The authors assessed mortality between January 1st 1987 and December 31st 1996, meaning that the participants were actually followed from the year 1987 to the year 1996; a period of 10 years. The authors have not stated anything about loss of follow-up as well as any efforts that were made to reduce loss to follow-up. The authors estimated exposure to nitrogen dioxide, particulate matter, black smoke and other traffic-related air pollutants at the home address of the subjects.
Type of Data Analysis: the authors analyzed the effects of air pollution for overall concentrations, and a mixture of background concentrations and traffic variables for the purpose of identifying effects of living close to busy highways separately. They calculated relative risks for concentrations and traffic variable dissimilarities between the 95th and 5th percentiles of the distributions (Beelen et al., 2008). The authors performed Cox analyses in the entire cohort with the use of Cox proportional hazards models. They computed person-years for every subject from baseline until end of follow-up or death. The authors adjusted for smoking, sex, age, as well as area-level. Cox-Poisson random effects survival software was used in incorporating spatial clustering at the neighborhood and/or municipal scale in the entire cohort analyses (Beelen et al., 2008).
Results/Main Findings of Study: the intensity of traffic on the closest road was independently linked to mortality. Relative risks at 95 percent CI for a 10-µg/m3 rise in the concentrations of black smoke – difference between 95th and 5th percentile – were 1.05 for natural cause, 1.03 for lung cancer, 1.22 for respiratory, 1.04 for cardiovascular, and 1.04 for mortality besides lung cancer, respiratory, or cardiovascular. The results were the same for PM2.5 and NO2, but there was no association for SO2 and mortality
Assessment of Bias: The authors selected subjects who were living near busy roads in 204 municipalities across the Netherlands. Those who lived far from busy highways were not chosen.
Assessment of Confounders: analysis in the case-cohort sample illustrated little distinction between the effect estimates adjusted for every confounder and adjusted for only the narrow set of confounders that were available in the entire cohort. The effect estimates were not sensitive to dissimilar models of confounders for both the case cohort and full cohort analyses.
Comments: The study is of major importance in contributing to the evidence that continuing and lasting exposure to traffic-related air pollution is linked to increased mortality. This is because traffic-related air pollution in addition to other traffic exposure variables were found to have an association with mortality in the cohort
References
Beelen, R., Hoek, G., Van Den Brandt, P., Goldbohm, R., Fischer, P., & Schouten, L. (2008). Long-term effects of traffic-related air pollution on mortality in a Dutch cohort (NLCS-AIR Study). Environmental Health Perspectives, 116(2), 196-202.
Gehring, U., Heinrich, J., Kramer, U., Grote, V., Hochadel, M., Sugiri, D. (2006). Long-term Exposure to Ambient Air Pollution and Cardiopulmonary Mortality in Women. Epidemiology. 17:545–651.
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