Harmonised datasets on asthma open up new research opportunities

Harmonised data on asthma from five UK cohort studies 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 asthma collected from study participants born in 1946, 1958, 1970, 1989-90 and 2000-02. Together, these new harmonised datasets can show the prevalence of asthma across people’s lives, based on their own reports and information from parents and doctors.

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

These harmonised datasets will allow researchers to combine and compare data from longitudinal studies, increasing the statistical power of analyses and enhancing cross-cohort research about people’s experiences of asthma across generations.

What’s included in the new datasets?

The researchers harmonised data to create new variables about diagnoses of asthma among study participants at specific sweeps and also harmonised information from across sweeps, using data from the following UK cohort studies:

• The MRC National Survey of Health and Development (NSHD) – 5,362 people born in England, Scotland and Wales during one week of 1946.
• The 1958 National Child Development Study (NCDS) – 17,415 people born in England, Scotland, or Wales in a single week in 1958.
• The 1970 British Cohort Study (BCS70) – 17,198 people born in England, Scotland, and Wales in a single week of 1970.
• Next Steps – 16,000 people in England born in 1989/90.
• The Millennium Cohort Study (MCS) – 19,517 children born in England, Scotland, Wales, and Northern Ireland in 2000-2002.

The sweep-specific harmonised variables combine data from three main areas. These include:

• Direct questions about lifetime prevalence of asthma: including whether the cohort member has ever had asthma, or whether they have had asthma since the previous sweep (in which case these responses can be combined with those from previous sweeps to derive lifetime prevalence).
• Direct questions about current asthma: including if they currently have asthma at the time of the sweep, or in the last 12 months.
• Other questions that may provide additional information on recent occurrence of asthma: including questions about any longstanding illnesses where a cohort member reports a condition which is then coded using the International Classification of Diseases (ICD).

The new datasets also include information harmonised from across survey sweeps to create a variable that indicates whether participants had ever reported asthma up to a certain time point. These cumulative ‘ever’ reported asthma indicators include information from all sweeps where questions on asthma have been asked.

The datasets focus on harmonised variables from questions that were administered to entire cohorts only and do not include information from biomarkers and linked health data.

For BCS70 and NCDS, questions for asthma were systematically combined with wheezy bronchitis at certain time points (e.g. ‘Have you ever had asthma or wheezy bronchitis?’ ‘Do you currently have asthma or wheezy bronchitis’).

Therefore, wherever possible, the researchers attempted to create an additional indicator variable for ‘asthma and wheezy bronchitis’ grouped together. This applies also to survey sweeps where asthma and wheezy bronchitis were reported separately (including for NSHD, Next Steps and MCS during the Covid-19 surveys), in which case they created indicator variables for asthma alone, as well as for asthma and wheezy bronchitis grouped together.

Why this new data is important

Dr Martina Narayanan (UCL Centre for Longitudinal Studies) said: “Asthma is an increasingly common health-related condition with an estimated eight in 100 people in the UK living with diagnosed asthma.”

“By harmonising these data, we can improve the accuracy and comparability of information collected on asthma. Researchers will be able to undertake cross-cohort analyses more easily to build a clearer picture about asthma over the life course, identifying risk factors and the related short and long-term outcomes of asthma. These new harmonised datasets can improve our evidence base on chronic health conditions helping to inform policy and practice and improving public health and wellbeing.”

How to access the data

The NCDS, BCS70, Next Steps and MCS harmonised asthma 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 asthma 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 asthma data alongside other information held for 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 a data access form 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 asthma datasets is available in the CLS user guide – Harmonised indicators of self-reported asthma in five British cohort studies.

Watch the training webinar

If you are interested to learn more about the harmonised asthma datasets, then watch the recording of the latest CLS training webinar hosted on 12 June 2025. You’ll hear about the methods being used to harmonise these measures, get practical guidance on how to access the data so you can you use it in your own research and learn about some examples of substantive research being conducted at CLS using these.

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