Calculation of Odds Ratio (OR) / Relative Risk (RR)

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	a + b + c + d 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