What is the definition of Mitotic Index? Sometimes I find Mitotic Index defined as (i) the number of dividing cells over the **number of non-dividing cells** , other times as the (ii) the number of dividing cells over the **total number of cells**... When reading a paper, which definition is more likely to be correct?

According to cancer.gov, it's the **ratio** of number of dividing cells to the number of cells not undergoing mitosis. This is equivalent to the number of dividing cells **over** the total number of cells.

Note that most papers, such as this one, report the mitotic index as a value from 0-100 (I.E. a percentage)