Which of the following is calculated by dividing the ratio of exposed subjects to nonexposed subjects in the case group by the ratio of exposed subjects to nonexposed subjects in the control group?

Atampa surgeon, dr. floyd legatron, mistakenly removed the wrong leg of 52-year-old jameson kingsmith during an amputation procedure in june of 2009. apparently, a chain of errors led to the mishap, and the surgical team even realized their error halfway into surgery, but by that time it was too late, and the leg had to be removed.