A study was undertaken to investigate the effect of asbestos exposure on lung cancer among employees at Factory A. In 2016, a group of 35,091 employees who worked at the factory from 1968 to 1994 and had cancer follow-up data available through 2015 were included in the study. Asbestos exposure was defined categorically based on whether the employee worked on site(exposed) or in the management building nearby (unexposed). The incidence rate among thosewho worked on site was then compared to the incidence rate among those who did not. Whichtype of epidemiologic study design is described above

Cohort study

Explanation:

There are 3 main classes of epidemiologic studies: 1-Cross-sectional studies; 2- Case-control studies; and 3- Cohort studies. Cross-sectional studies (also known as prevalence studies) involve looking at data possible factors of risk and disease outcomes from a given population at one specific point in time. Moreover, a case–control study is an observational study where two groups are identified and subsequently compared to identify possible factors associated with a medical condition. Finally, a cohort study initially classifies the subjects of study into two different groups depending on their exposure status and then the occurrence of the outcome of interest is assessed. In consequence, the example above described refers to a cohort study because this study examines a cohort (i.e., workers) that were classified by their exposure to asbestos, and then analyzes the incidence rate of cancer as the outcome.