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Closer - The home of longitudinal research

Data harmonisation

Data harmonisation involves recoding or modifying variables so that they are comparable across research studies.

What does harmonising data involve and why is it important?

In order to make full use of the cohort and longitudinal studies that we have in the UK, we need to be able to make comparisons both within and across studies. Repeating the same longitudinal analysis across a number of studies allows researchers to test whether results are consistent across studies, or differ in response to changing social conditions.

Cross-study analysis helps us understand more about societal change and how changes in the policy environment impact on outcomes for individuals.

What are the challenges?

Different studies have used different methods to collect information on important aspects of respondents’ lives. For example, measures of household income and measures of some senses, such as vision, are collected in quite different ways both within the studies over time and crucially, across the separate studies.

What is CLOSER doing about it?

Under the data harmonisation work stream, CLOSER is currently working on projects across multiple research themes to produce new data resources including guides to cross-study data comparability and harmonised datasets.

The harmonised datasets are made available to download from the UK Data Service, some with special licence access.

For more details on the different projects, see the research themes below:

Related projects

Earnings and income

This project investigated how families transfer wealth and advantage across generations by harmonising measures of earnings and income in four CLOSER studies.

Occupation and education

This CLOSER research examined how social background has influenced the educational attainment and careers of generations of British people, by harmonising measures of socio-economic status and educational attainment.

Body composition

This CLOSER research explored how rates of overweight and obesity are changing across generations. To do this it harmonised different measures of body size and composition, including height, weight and body mass index (BMI), across five longitudinal studies.


This project will help researchers examine the relationship between diet and health with ageing by documenting and comparing available dietary intake information across eight CLOSER studies.

Physical activity

This project is utilising data from six CLOSER studies to explore whether levels of physical activity vary by age, sex and ethnicity.

Mental health

This project aims to harmonise existing mental health measures over the life course in five British birth cohorts; the 1946, 1958, 1970, 2000-01 cohorts & ALSPAC.

Documenting mental health measures

This CLOSER research project will be the first to comprehensively document measures of mental health and wellbeing within the UK’s longitudinal studies.


This project will help researchers to more accurately explore the links between cognitive ability, social background and education.


This project produced a comparative catalogue of the biomarkers available across six CLOSER studies.

Analysing biological samples

This project explored how the collection, processing and storage conditions of biological samples could be made more consistent across longitudinal studies.

DNA methylation

This project aims to help researchers identify time periods over the lifecourse when people are most vulnerable to disease.

Pubertal status

This project assessed measures used to determine pubertal status, identifying similarities among methods that would allow harmonisation across cohorts

Visual health

This CLOSER research compared the visual health of different generations of British people for the first time by harmonising measures of visual function across three longitudinal studies.

Childhood adversity and adult wellbeing

This project explored associations between childhood social environment and adult mental wellbeing to examine whether the relationship between the two has changed across different generations.

Socio-economic status in ALSPAC

Researchers are producing new documentation and data to help researchers interested in socio-economic status and how it changes over time among those taking part in ALSPAC.

Household overcrowding

This research investigated household overcrowding across generations, by producing comparable measures from information collected by five CLOSER studies.