Table 1.

Illustration of the Possible Definitions of 2-Way Interactions With 1 Binary Exposure and 2 Binary Mediators

Varying Argument	Interaction Definition
A·M1 varying, M2 = 1	p(111) − p(101) − p(011) + p(001)
A·M1 varying, M2 = 0	p(110) − p(100) − p(010) + p(000)
A·M2 varying, M1 = 1	p(111) − p(110) − p(011) + p(010)
A·M2 varying, M1 = 0	p(101) − p(100) − p(001) + p(000)
M1·M2 varying, A = 1	p(111) − p(110) − p(101) + p(100)
M1·M2 varying, A = 0	p(011) − p(010) − p(001) + p(000)

Abbreviations: A, exposure of interest; M, potential mediator.