Two SNPs Associated With Spontaneous Dizygotic Twinning: Effect Sizes and How We Communicate Them.

In a recent GWAS of spontaneous dizygotic twinning, Mbarek et al. (The American Journal of Human Genetics, 2016, Vol 98, pp. 898-908) identified two SNPs, rs11031006 (near FSHB) and rs17293443 (in SMAD3). In the present note, we address the question how to present the results in terms of effect sizes in a manner that is comprehensible to the general audience (e.g., mothers of twins, readership of newspapers). We propose to avoid the standard effect sizes such as odds ratios and relative risk as these require some knowledge of probability theory. Rather, we convey the results in terms of the conditional probabilities, but expressed in natural language.