tailieunhanh - Ebook Applied epidemiologic principles and concepts - Clinicians’ guide to study design and conduct : Part 2
Part 2 book “Applied epidemiologic principles and concepts - Clinicians’ guide to study design and conduct” has contents: Ecologic studies - Design, conduct, and interpretation, case-control studies, cross-sectional studies, cohort studies, causal inference in clinical research and quantitative evidence synthesis, and other contents. | 7 Ecologic studies Design, conduct, and interpretation Introduction Ecologic studies are sometimes not understood in epidemiologic or medical settings due to the limited or low frequency of its utilization in evidence discovery. Ecologic designs reflect investigations in which the unit of observation is the group and the analysis is performed on the group and not individual level. This design is feasible in assessing an association when the exposure and outcomes are available on the group level. In this context, ecologic studies may serve the purpose for generating hypothesis for individual-level studies. Often, data are available on aggregate measure of the exposure and outcome of interest. Additionally, causal association with ecologic design is difficult to establish. Assuming that prostate cancer (CaP) mortality is higher in zip code 19810 with lower level of pesticide exposure relative to 19960 with higher pesticide exposure, does this design imply the protective effect of CaP mortality by pesticide exposure? Such an inference cannot be drawn given the reality of population dynamics in terms of migration since CaP mortality in 19810 may be due to CaP patients or individuals moving to 19810 from 19960 and other zip codes with higher levels of pesticides. Also, such a design restricts the individual-level data on confounding in addressing the confounding effect of comorbidity, income, education, etc., factors observed to influence CaP mortality. This chapter describes ecologic design as group level or aggregate data study design, presenting hypothetical and real-world examples (Figure ). The different types of ecologic designs are presented as well as ecologic fallacy. The advantages and limitations of ecologic design are addressed, notably confounding as a mixing effect of the third variable in the association between the exposure and the outcome of interest. The advantages include public access data, low-cost data acquisition, and the feasibility of
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