Research on fertility and families enhanced with new harmonised cohort data

Harmonised data on the fertility histories of four British cohorts are now available for the scientific community to download from the UK Data Service.

The UCL Centre for Longitudinal Studies (CLS) has harmonised data on fertility histories collected from four generations of people born in 1946, 1958, 1970, and 1989-90. These new harmonised datasets bring together information on partnerships, childbearing and family formation reported by study participants throughout their adult lives.

Harmonisation is a process of recoding or standardising variables that were collected in different ways so that survey data are comparable across studies, or across multiple sweeps of the same study.

These harmonised datasets allow researchers to combine and compare data from the four British cohorts, enhancing cross-cohort research to more accurately compare fertility and family life across generations.

What’s included in the new datasets?

The researchers harmonised data from the following British cohort studies to create derived variables about fertility histories:

• The MRC National Survey of Health and Development (MRC NSHD): 5,362 people born in England, Scotland and Wales during one week of 1946 with fertility histories reported between age 19 and 53.
• The 1958 National Child Development Study (NCDS): 17,415 people born in England, Scotland, or Wales in a single week in 1958 with fertility histories reported from age 23 to 50.
• The 1970 British Cohort Study (BCS70): 17,198 people born in England, Scotland, and Wales in a single week of 1970 with fertility histories reported between age 26 to age 51.
• Next Steps: 16,000 people in England born in 1989-90 with fertility histories reported at age 25 and 32.

The new datasets include information harmonised from across sweeps for each cohort study. The derived variables provide a summary of partnership status, childbearing and family structure for women and men who participated at each sweep, including information on:

• marital status
• whether has a partner in household
• whether they have had any children, including biological and adopted, fostered and stepchildren
• children in the household
• age when they had children
• number of children
• age of the eldest and youngest child
• number of boys and girls.

The focus was on live births rather than pregnancies that were terminated, miscarriages, or stillbirths.

Due to lack of information, it was not possible to derive all target variables, at all sweeps, in all cohorts. The NSHD especially was affected by this, whereas a larger number of harmonised variables could be derived in the NCDS, BCS70, and Next Steps, which share many identical survey questions.

Why this new data is important

Dr Aase Villadsen (UCL Centre for Longitudinal Studies) said: “These new harmonised datasets on the fertility histories of four generations of British people can be linked to a rich range of other variables across the cohort studies, opening up new opportunities for research on fertility and family formation. For example, as these new data include information for both females and males, they can help close the gap in our knowledge on men’s fertility.

“As many experts weigh up the repercussions of declining fertility rates for the economy and society, these new data have the potential to improve the scope and accuracy of information about births in Britain, enhancing future research on fertility trends, and informing policymaking and government planning.”

How to access the data

The NCDS, BCS70 and Next Steps harmonised datasets are available from the UK Data Service (UKDS) website under an end user licence agreement.

The NSHD dataset can be accessed by downloading the UKDS Special Licence application form. Once the form has been reviewed by UKDS and approved by the NSHD Data Sharing Committee the data will be available to download. Find out more on the UK Data Service website.

The NSHD fertility histories dataset is also available from MRC Unit for Lifelong Health and Ageing at UCL (LHA), which manages the NSHD. This route of access is necessary for analysts wishing to use the fertility data alongside other information held from the 1946 cohort. The research project needs to first be approved by the NSHD Data Sharing Committee. Full details on how to access the data can be found on the NSHD Skylark website. Once data access has been approved and a data sharing agreement is in place, the data can be accessed via the NSHD Data Sharing website.

Find out more

Further information about the harmonised fertility histories datasets is available in the CLS user guide:  Fertility histories in four British cohort studies.