Millennium Cohort Study

The Millennium Cohort Study (MCS), known as ‘Child of the New Century’ to cohort members and their families, is following the lives of around 19,000 young people born across England, Scotland, Wales and Northern Ireland in 2000-02. The study began with an original sample of 18,818 cohort members.

What’s in the study?

MCS provides multiple measures of the cohort members’ physical, socio-emotional, cognitive and behavioural development over time, as well as detailed information on their daily life, behaviour and experiences. Alongside this, rich information on economic circumstances, parenting, relationships and family life is available from both resident parents.

National Pupil Database (NPD) records have also been linked to the MCS data, including GCSE exam results.

What has the study found?

MCS has provided important evidence to show how circumstances in the very first stages of life can influence later health and development.

Research based on MCS has shown that the likelihood of being breastfed is affected by which day in the week a child is born, which has strong subsequent effects on cognitive development.

MCS has also found that school admissions policies disadvantage children born in the summer months, affecting their performance in cognitive tests as well as their non-cognitive skills, and that children born in the summer months were more likely to be placed in lower ability groups than their autumn-born peers.

The study has contributed crucial evidence on two major health issues facing this generation; the high rates of both mental-ill health and obesity among this age group, now in their teens.

Who funds the study?

MCS is core funded by the Economic and Social Research Council and a consortium of government departments.

MCS sweeps

We have completed seven MCS sweeps to date. The Age 23 sweep is now underway. Click on a sweep below to learn more about the information collected.

Watch the webinar: Introduction to MCS

COVID-19 survey and data

Data from all three waves of our survey of five national longitudinal cohort studies, including MCS, are now available. Find out about the topics covered, response and how to access the data.

Find out more

Sub studies

In addition to the main MCS sweeps there have been a number of sub studies. You can find out more about these on the following pages:

Latest from MCS


Families and relationships in four British cohort studies: measurement, research and access

1 October 2024

This webinar highlights some examples of research on families and relationships using CLS’ unique series of UK national cohort studies.


Improving the nation’s numeracy: what can we learn from the British cohorts?

4 July 2024

What can cohort evidence tell us about the predictive power of early maths skills and what policymakers can do to boost the nation’s numeracy?


Blog: being excluded or truant from school leads to mental health problems – and vice versa

5 March 2024

New research shows children who struggle with their mental health are more likely to later be excluded from school and to truant. And exclusion and truancy can increase their mental health difficulties.


Body dissatisfaction linked with depression risk in children

15 February 2024

Body dissatisfaction at age 11 is linked to increased risk of depression by age 14, according to new research from the Millennium Cohort Study.

Initial findings from the Age 17 Sweep

Here you can read our initial findings from the Age 17 Sweep. These examine a range of issues, including mental health, obesity, substance use and antisocial behaviour.

Find out more about our initial findings

Cohort profiles

Joshi, H and Fitzsimons, E
The Millennium Cohort Study: the making of a multi-purpose resource for social science and policy
Longitudinal and Life Course Studies, volume 7, issue 4, 2016
Read the full paper
Connelly, R and Platt, L
Cohort Profile: UK Millennium Cohort Study (MCS)
International Journal of Epidemiology, volume 43, issue 6, December 2014, pages 1719–1725
Read the full paper

Special features of this study

Sample design

Unlike the previous three national birth cohorts, which all share the same birth week, MCS cohort members were born over a 17 month period (September 2000-January 2002). This allows researchers to investigate season of birth effects in children’s outcomes and trajectories.

The population from which every child should have a known, non-zero chance of selection was defined as: all those:

  • born within eligible dates: between 1/9/2000 and 31/8/2001 (England & Wales), and between 23/11/2000 and 11/01/2002 (Scotland and Northern Ireland),
  • alive and living in the UK at age nine months and
  • eligible to receive Child Benefit at that age.

The sampling strategy was to make a selection of areas of residence, and within them to recruit 100 per cent of the children born in the eligible period. The statistical geography available for such clusters in 2000-01 was the boundaries of electoral wards as they stood before updating at the 2001 census.

Importantly, certain sub-groups of the population were intentionally over-sampled, namely children living in disadvantaged areas, children of ethnic minority backgrounds and children growing up in the smaller nations of the UK.

By the end of fieldwork for the Age 9-Months Sweep, 18,552 families had been interviewed, and the cohort included 18,818 children, allowing for 246 sets of twins and 10 sets of triplets. This represents a response rate of 72 per cent of all the families with eligible children living at nine months in the sampled wards.

The Age 3 Sweep in 2003-04 provided an opportunity to catch up with families who should have been in the Age 9-Months Sweep, but had been missed because they had only recently moved to an eligible address. This group of ‘new families’ was only recruited in England. The boost to the sample from the ‘new families’ brought the total of all families ever interviewed to 19,243 (and the number of children ever taking part up to 19,517).

There is no sample refreshment by immigrants. All the MCS children were resident in the UK at nine months, and would cease to be eligible if they leave the UK (but resume eligibility on return to the UK).

For further details, please see Plewis (2007).

Biomedical data

Objective physical measurements have been taken since the age of 3. They include height, weight, waist measurement and body fat.  At ages 7 and 14, activity monitors were worn in order to measure physical activity and sedentary behaviour.

At age 14, cohort members and their residential natural parents were asked to provide a saliva sample for DNA extraction and subsequent genotyping. This is the first time a triad of DNA samples has been collected from 2 biological parents and their child in a large scale nationally representative study.

Linked administrative data

Administrative data from relevant government departments and agencies have been linked to the survey data in the domains of health and education. The data are available to access through the UK Data Service. Up to age 16, these linkages are based on parental consent collected at various time points. At age 17, we asked cohort members for their own consent.

Linked health data are available from birth registration records and maternity records based on parental consent shortly after birth. We are working to link Hospital Episode Statistics (HES) for England and have already linked some health data for Scotland and Wales.

Linked health data are available from Scottish Medical Records (SMR) for 2000-2015 (outpatient, inpatient and day care, maternity, Prescribing Information System).

For Wales the number of inpatient and day case hospitalisations at ages 0-11 are available. A range of Welsh health records up to cohort members’ 14th birthdays can also be linked to the cohort data through the SAIL Databank, including Child Health, Emergency Department, Patient Episode Database and Primary Care GP data.

For cohort members in England, pupil-level linked education data from the National Pupil Database are available for Key Stages 1, 2 and 4, including exam results as well as information on absences, ethnicity, languages spoken at home, special educational needs, and eligibility for free school meals. School-level data are also available.

For Scotland and Wales, Key Stage 1 data are available through UKDS. For Wales, education records up to and including Key Stage 4 can also be linked to cohort data through the SAIL Databank.

Future data linkage
At age 17, cohort members were asked for their permission to link data from an extensive range of administrative records to the MCS survey data. These include information on:

  • health (from hospital records)
  • education and training records after age 16
  • higher education applications and offers
  • payments of student loans
  • records kept by the Department for Work and Pensions and HM Revenue & Customs, including about benefit claims, participation in employment programmes, jobs, earnings, tax and National Insurance
  • crime records.

We are pursuing these linkages with the aim of making the linked administrative data, including data currently only accessible through the SAIL Databank, available via the UK Data Service. We are currently applying to link to HES data which will include COVID-19 data and plan to refresh the SMR linkages.

Cognitive assessments

The MCS has been carrying out cognitive assessments with cohort members since the age of three, using leading standardised age-appropriate assessments such as the British Ability Scales.

Assessments range from measuring preschool knowledge of numbers, letter, shapes and sizes through numeracy and vocabulary to non-verbal assessments of pattern construction and touch screen measures of spatial working memory and decision making. They provide objective measures of the cohort members’ numeric and linguistic abilities, and how they develop across childhood and adolescence.

Information from fathers

Data has been collected from resident fathers, including step-fathers, as well as from mothers at all sweeps. This was an innovation for a national cohort, and reflected strong scientific interest in the role of fathers and the increasing diversity of family life in the UK.

Popular survey documentation

MCS 9 Months-Age 11 Guide to the Datasets (Eighth Edition)

Eighth edition of MCS User Guide to the Datasets

Authors: Kristine Hansen
Date published: February 2014
PDF: 934,04 KB


MCS Age 14 survey- User guide

The user guide accompanying the Age 14 survey.

Authors: Emla Fitzsimons
Date published: February 2017
PDF: 1,36 MB


Data access

We’ve published guidance to help users find out what’s in our data.

Most MCS data are available through the UK Data Service. Visit the UK Data Service study page for MCS [SN 2000031].

Some of the linked education and health data for Wales are currently only available through the SAIL Databank with plans to also deposit them with the UK Data Service.

Principal Investigator

Emla Fitzsimons Professor of Economics and Director of the Millennium Cohort Study

Phone: 020 7331 5129

Emla is the Director of the UK Millennium Cohort Study, a longitudinal birth cohort study following children born at the turn of the new century. Her research is focused on the development of human capital throughout the life course, and in particular how experiences and circumstances in early life and childhood affect causally the acquisition of skills later on.

Contact us

Centre for Longitudinal Studies
UCL Social Research Institute

20 Bedford Way
London WC1H 0AL


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