I don't agree with everything in this paper but it does provide some useful information.
VanderWeele, Tyler J. (2010) "Epistatic Interactions," Statistical Applications in Genetics and Molecular Biology: Vol. 9 : Iss. 1, Article 1. [PDF]
The term "epistasis" is sometimes used to describe some form of statistical interaction between genetic factors and is alternatively sometimes used to describe instances in which the effect of a particular genetic variant is masked by a variant at another locus. In general statistical tests for interaction are of limited use in detecting "epistasis" in the sense of masking. It is, however, shown that there are relations between empirical data patterns and epistasis that have not been previously noted. These relations can sometimes be exploited to empirically test for "epistatic interactions" in the sense of the masking of the effect of a particular genetic variant by a variant at another locus.