The relative importance of nature, nurture & peer effects on adult outcomes: Full research report ESRC end of award report, RES-000-22-1545

This project developed a relatively underused aspect of the National Child Development Study (NCDS) and the British Cohort Study (BCS70) data sets, that of the data on twins. It attempted to develop better measures of zygosity (whether the twins were identical or not) as the previously available data was collected at birth as recorded by the medics, who most likely but not definitely based this decision on the number of placenta which can substantially underestimate the number of identical twins (Bryan 1992). Previous work using the twins of the cohort studies had either not required the data on the zygosity of twins or had been based on the unreliable available data (Annett 1987, Blanchflower and Elias 1999, Emanuel et al 1992). As well as hoping to enhance the quality of the zygosity of the twins, this project proposed a hypothesis which could be used to verify the usefulness of the data. The hypothesis was, as suggested in the title, to test the relative importance of nature, nurture and peer effects on adult outcomes, focusing on education and labour market success. This hypothesis was proposed in response to two high profile publications such as Herrnstein and Murray (1996) which suggested educational success was mostly genetic and Harris (1999) which suggested educational success was mostly peer related. It was hoped that the data on twins from the cohort study would be able to shed some light on this topic. Finally the additional benefit of the cohort studies compared to other twin data sources previously used by the PI was the availability of a range of peer measures available on the cohort studies (Hawkes 2003). Whilst data on peers could have been collected from twins of the St. Thomas’ Twin Register these would have been subject to recall bias as the collection of the data would have occurred now the twins are in adulthood. The longitudinal nature of the cohort studies means that data collected on peers was collected at various points in childhood and therefore not subject to recall bias.