TY - JOUR AU - Røysamb, Espen AU - Tambs, Kristian PY - 2016/07/20 Y2 - 2024/03/28 TI - The beauty, logic and limitations of twin studies JF - Norsk Epidemiologi JA - Nor J Epidemiol VL - 26 IS - 1-2 SE - DO - 10.5324/nje.v26i1-2.2014 UR - https://www.ntnu.no/ojs/index.php/norepid/article/view/2014 SP - AB - During the last fifty years more than 2700 twin studies have been published, examining the etiology of a<br />high number of traits. Twin studies enable investigation of both genetic and environmental effects, and<br />thereby also examination of causal factors involved in human traits and disorders. The beauty of twin<br />studies resides in the potential of studying the unobserved by the logic of a design. The aim of this article is<br />to outline central theoretical foundations and possible limitations, and to review selected key findings. We<br />describe the inherent fundamentals of the classic and extended twin designs. The logic of the main analytic<br />approaches is outlined, and the principles of univariate biometric modelling described. Next, we review<br />different multivariate models, including the Cholesky, correlated factors, common factor, common pathway<br />and phenotypic causality models. Additionally, the cotwin-control approach, representing a natural<br />experimental design, and mimicking a counterfactual situation, is outlined. Central assumptions, threats<br />and limitations of the twin design are discussed. In particular, we address the issue of missing heritability,<br />non-random mating, the equal environment assumption and gene-environment correlations. Finally, we<br />review some selected findings from the field of behavior genetics and twin studies. ER -