Table 2.

An example of a study with cases and non-cases

Environment (E)	Susceptibility (S)	Disease	No disease	Total	Relative Risk (RR)	Odds Ratio (OR)
–	–	a	B	a + B	1.0 (ref)	1.0 (reference)
–	+	c	D	c + D	RRs=$\frac{\mathrm{c}\left(\mathrm{a},+,\mathrm{B}\right)}{\mathrm{a}\left(\mathrm{c},+,\mathrm{D}\right)}$	ORs=$\frac{\mathrm{cB}}{\mathrm{aD}}$
+	–	e	F	e + F	RRe=$\frac{\mathrm{e}\left(\mathrm{a},+,\mathrm{B}\right)}{\mathrm{a}\left(\mathrm{e},+,\mathrm{F}\right)}$	ORe=$\frac{\mathrm{eB}}{\mathrm{aF}}$
+	+	g	H	g + H	RRse=$\frac{\mathrm{g}\left(\mathrm{a},+,\mathrm{B}\right)}{\mathrm{a}\left(\mathrm{g},+,\mathrm{H}\right)}$	ORse=$\frac{\mathrm{gB}}{\mathrm{aH}}$

Under additive scale: ICR_c/nc = RR_se-(RR_s + RR_e-1), ICR_c/nc = OR_se-(OR_s + OR_e-1)

Under multiplicative scale: ICR_c/nc = RR_se/(RR_s × RR_e), ICR_c/nc = OR_se/(OR_s × OR_e)