The Environmental Risk (E-Risk) Longitudinal Twin Study aims to build knowledge around the question of how environmental and genetic factors contribute to the development of behaviors, health and mental health problems from childhood through to adulthood. In 1998, E-Risk began by constructing a nationally representative two-year birth cohort of 2,232 same-sex twins born in England and Wales in 1994-1995. The study recruited families to represent the UK population with newborns in the 1990s, to avoid an excess of twins born to well-educated women using assisted reproduction and to ensure adequate numbers of children from disadvantaged homes.
The resulting study sample represents the full range of socioeconomic conditions in Great Britain; the families’ distribution is reflected on a neighborhood-level socioeconomic index (ACORN) that very closely matches the national distribution. The longitudinal study has concentrated on three developmental stages to date: (1) the transition to formal schooling, with assessments at ages 5 (1999-2000) and 7 years (2001-2002), retaining 98% of the cohort, (2) the transition to secondary school, with assessments at ages 10 (2004-2005) and 12 (2006-2007), retaining 96% of the cohort and (3) the transition to young adulthood, with assessments at age 18 (2012-2014), retaining 93% of the cohort. Home visits to participants before age 18 included assessments with primary caretakers as well as the participants whereas the visits at age 18 included interviews only with participants.