Kaksosmalli

Kaksosmalli is a statistical research design used in behavioral genetics to separate genetic and environmental influences on variation in traits by comparing monozygotic (identical) and dizygotic (fraternal) twins. The model partitions trait variance into components, most commonly additive genetic factors (A), shared environmental factors (C), and non-shared environmental factors (E). Some variants include dominant genetic effects (D), yielding ACE, ADE, AE, or CE models. Because monozygotic twins share nearly all their genes while dizygotic twins share about half, differences in trait similarity between the two groups provide estimates of heritability and environmental contributions. Structural equation modeling is a typical analytic approach for fitting these models to data.

Data for kaksosmalli come from twin samples with known zygosity, where researchers measure relevant traits and estimate the proportion of variance explained by A, C, and E. The results commonly reported are heritability estimates and confidence intervals, along with insights into the role of shared and non-shared environments.

Applications of the kaksosmalli span psychology, psychiatry, behavioral genetics, and related fields. It has been used to study cognitive abilities, personality, mental health conditions, physical traits such as height, and responses to interventions. The design helps researchers gauge the relative importance of genes and environment, though it relies on assumptions such as the equality of environments for twins and can be limited by measurement error or assortative mating. Extensions to the basic design, such as augmented twin-family designs, broaden the scope to explore gene–environment interactions and developmental trajectories.