Researchers reviewed the insurance records of 3,250 workers of the local rubber manufacturing plant who have worked at the facility for at least 20 yrs as of Dec. 1997. Of these workers, 1,210 were occupational exposed to asbestos and the remainder were not. A subsequent search of these workers' death records found that 675 of them were exposed to asbestos had died from lung related diseases. This is an example of? Question 11 options: Ecological Study Prospective Cohort Study Case Control Study Retrospective Cohort Study