. 2020 Jun 4;49(4):1259–1269. doi: 10.1093/ije/dyaa065
© The Author(s) 2020. Published by Oxford University Press on behalf of the International Epidemiological Association.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Figure 1.
Possible causal diagrams for two measured traits X and Y for twins.