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Which term most accurately describes the following definition? \"Analysis based on aggregated or grouped data; errors in inference may result because associations may be artifactually created or masked by the aggregation process.\" [Porta M, ed. A Dictionary of Epidemiology. New York: Oxford University Press; 2014.] a) Ecologic study b) Cohort study Od Cross-sectional study ) d) Case-control study e) Randomized trial