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Twin-based study of the complex interplay between childhood maltreatment and socioeconomic status and their effects on adult memory
Ximena Goldberg1, Silvia Alemany1, Mar Fatjó-Vilas1, Itxaso González-Ortega2, Ana
González-Pinto2, Manuel J. Cuesta3, Lourdes Fañanás1
Corresponding author: Lourdes Fañanás, Departament de Biologia Animal, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, Edifici Margalef 2n pis, 08028 Barcelona, Spain. E-mail: firstname.lastname@example.org
The effect of childhood maltreatment on memory was decomposed into that owing to within-pairs differences of childhood maltreatment total scores and that responding to between-pair differences (Carlin et al., 2005). The formulation of this model was:
Yij = β0 + βw (Xij –i) + βb i
Where Y denotes the outcome (memory performance during adulthood), X the covariate of interest (childhood maltreatment total score), i twin pairs and j individual within twin pair. i represents the mean value of childhood maltreatment for twin pair i. The within-pair coefficient βw gives the expected change in memory performance in adulthood for a one-unit change in the difference between the individual X and the twin-pair average of childhood maltreatment, while holding the latter constant.
Given that this analysis was performed in genetically identical monozygotic twins, βw represents an association that is free of confounding due to factors that are common to the two twins, and therefore is a measure of unique environmental effects of childhood maltreatment on the association. The between-pair coefficient βb gives the expected change in memory performance for a one-unit change in the twin-pair average of childhood maltreatment total score, while holding the individual deviation from the average constant. It provides a measure of family-wide (both genetic and environmental) effects on the association (Johnson et al., 2009).