Twins study

Twin studies are often used to study the relative importance of nature versus nurture. BCS70 did not have particularly reliable information about zygosity (whether twins are genetically identical), which made it difficult to conduct this type of research with the information collected from BCS70 twins. As such, in 2008, a postal questionnaire was sent to all pairs of twins with a series of questions to allow zygosity to be accurately identified.

The study was undertaken as a part of the project The Relative Importance of Nature, Nurture, and Peer Effects on Adult Outcomes, funded by the Economic and Social Research Council.

The aims and objectives of the project were:

1. to provide a more complete and accurate dataset which identifies the zygosity (whether the twins were identical or not) of the twins in the NCDS and the BCS70
2. to use the data held on the twins in the NCDS and BCS70 to consider the relative importance of nature, nurture, and peer effects in childhood and adult outcomes such as education, employment, and earnings
3. to identify the relative importance of nature, nurture, and peer effects on each adult outcome across the two cohorts and within the two cohorts across time in order to assess whether and how these relative effects change over the life course and the stability or change in these patterns for people born at different times.

This questionnaire was developed based on existing instruments used by other twin studies, and covers self-reported zygosity, physical similarity, and widely used ‘peas-in-a-pod’ questions. A dataset was created from the collected questionnaires, containing three new measures of zygosity.