In 2000, the Mega factory employed 15,000 people, 5,750 were employed in areas exposed to ionizing radiation, while the remaining 9,250 were employed in other areas not exposed to radiation. In 2020, a research team conducted a study among these 15,000 workers. The team investigated the records of exposure status at the beginning of the study in 2000 and before. The entire cancer-free population of 15,000 was followed for 10 years to determine whether radiation exposure increased cancer development, and the disease status was collected from the cancer registry between 2000 and 2010, where they found that of the 5,750 workers exposed to radiation, 275 developed cancers, and of the 9,250 that were not exposed to radiation, 175 developed cancers.

E. What is the occurrence measure?