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 2000-01. The study began with an original sample of 18,818 cohort members.

What’s in the study?

The 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, so far including attainment up to  Key Stage 2, and updated linkage, up to GCSE (Key Stage 4) is underway.

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 six MCS sweeps to date. The most recent sweep was when cohort members were 14 years old. We are currently surveying them again, at age 17. Click on a sweep below to learn more about the information collected.


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:

Initial findings from the Age 14 Sweep

The most recent MCS survey took place when cohort members were 14. Our initial findings cover a range of issues relevant to young people’s lives today, from mental health to obesity and risky activities.

Find out more about our initial findings

Latest from MCS


Millennium Cohort Study a vital resource for children's advocates, explains the Children's Society in new film

10 October 2018 Childhood and adolescent mental health are the focus of a new short film from the UCL Institute of Education (IOE), launched today, World Mental Health Day (10 October 2018).

Children born premature just as physically active as their peers, new study finds

23 May 2019 Being born early is no barrier to children and adolescents participating in organised sports and playing with friends, according to new research.

Research round-up – January to March 2019

12 April 2019 Is screen time really behind the rise in teenage mental health problems? How is the ‘sandwich generation’ faring as they care for their ageing parents and their children and grandchildren? Researchers have been using CLS study data to tackle these and other key questions.

Mothers are not to blame for our childhood obesity crisis

25 March 2019 The number of obese children and teenagers across the world has increased tenfold over the past four decades and it is estimated that about one in four 14-year-olds in the UK is either overweight or obese.

Obesity and emotional problems tend to develop together as children age, new research shows

22 March 2019 High BMI and mental ill-health go increasingly hand-in-hand to present a combined health risk for children from mid-childhood, according to a new study.

Cohort profiles

These cohort profiles provide information about the background to the study as well as its sample size, content, and findings.

JOSHI, H and FITZSIMONS, E.  (2016)  The Millennium Cohort Study: the making of a multi-purpose resource for social science and policy.  Longitudinal and Life Course Studies, 7(4),  409-430.

CONNELLY, R and PLATT, L.  (2014)  Cohort Profile: UK Millennium Cohort Study (MCS). International Journal of Epidemiology, 43(6),  1719-1725.

Recent scientific publications

Fitzsimons, E and Villadsen, A
Father departure and children's mental health: How does timing matter?
Social Science & Medicine, 2018
Read the full paper
Sheldrake, R
Changes in Children’s Science-Related Career Aspirations from Age 11 to Age 14
Research in Science Education, 2018, pp1-30
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 has been linked to the survey data collected in the study in the domains of health and education.

Linked health data is available from birth registration records and maternity records. Linked educational data from the National Pupil Database, comprising Key Stage 1 and Key Stage 2 assessment scores, is also available.

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].

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 Institute of Education

20 Bedford Way
London WC1H 0AL