It has been suggested that occupational exposure to benzene in the petroleum industry increases the risk of developing leukemia. the levels of benzene to which workers in this industry have been exposed were high from 1940 to 1970, but since 1970 have been significantly reduced. what kind of study design, using petroleum workers, would provide the most useful information on whether benzene affects incidence rates of leukemia in this industry? you may assume that records of individual worker assignments to jobs involving benzene exposure have been maintained by the industry.

Retrospective cohort study

Explanation:

A cohort study is the study where people are grouped according to the factors they have been exposed to. The cohort is the group.

A retrospective cohort study is the study where the cohort who has been exposed to certain factors is compared with another cohort who has not been exposed to the factors that the first cohort has been exposed. This study is a long term study.

Here, the people's health of those that have been exposed to benzene will be compared to the the people who have been working there after 1970.

Hence, here a retrospective cohort study will be done.

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