Calculation of odds ratio/relative risk for the use of trimethoprim-sulfamethoxazole prophylaxis in cirrhosis:
| Adverse event occurs (infectious complication) |
Adverse event doesn’t occur (no infectious complication) |
Totals | |
|---|---|---|---|
| Exposed to the treatment (experimental) |
1 a |
29 b |
30 a + b |
| Not exposed to the treatment (control) |
9 c |
21 d |
30 c + d |
| Totals | a + c 10 |
b + d 50 |
60 |
CER = c/(c+d)= 0.30
EER = a/(a+b)= 0.033
Control event odds = c/d
= 0.43
Experimental event odds = a/b
= 0.034
Relative risk = EER/CER
= 0.11
Relative odds = odds ratio
= (a/b)/(c/d)
= ad/bc = 0.08
