The classic contingency.
| Exposure | Outcome (disease=D+) for example Tumor recurrence | No outcome (no-disease=D-) for example No tumor recurrence | Total |
|---|---|---|---|
| Intervention (exposed=E+) for example Dr. JJ’s new approach | Exposed with outcome =a (recurrent cases operated via Dr. JJ’s approach) | Exposed without outcome=b (non-recurrent cases operated via Dr JJ’s approach) | All exposed persons =a+b (all patients operated via Dr. JJ’s approach) |
| No intervention (non-exposed=E-) for example sub-frontal approach | Not exposed with outcome =c (recurrent cases operated via subfrontal approach) | Not exposed without outcome=d (non-recurrent cases operated via subfrontal approach) | All non-exposed persons =c+d (All patients operated via the subfrontal approach) |
| All persons with outcome =a+c (all patients with tumor recurrence) | All persons without outcome =b+d (All patients without tumor recurrence) | All persons a+b+c+d |
Risk or incidence of recurrence= a/a+b (for Dr. JJ’s approach) & c/c+d (for subfrontal approach), relative risk (RR)=[Risk in exposed]/ [Risk in the non-exposed]=[a/a+b]/ [c/c+d], odds of exposure in the cases=[a/c] and odds of exposure in the controls=[b/d], odds ratio (OR)=[odds of exposure in the cases]/[odds of exposure in the controls]=[a/c]/[b/d]