Children of the new century

At a basic level, what is this study about? What sorts of parameters you are measuring with these children?

This is a nationally representative study of a big cohort of children born in the UK at the turn of the millennium – around 2000 to very early in 2002. It started off with just over 19,000 children and families, and it's following their journeys through life in many domains. It's trying to understand how and when inequalities emerge in children's development, for instance; how children fare during their very early years; how the home environment matters; the importance of parenting; the importance of financial resources; and so on. And how that shapes their lives as they grow older.

It's also intended to provide a comparison with previous generations – it's the fourth UK longitudinal study, and the only one to include Northern Ireland. The first one began in 1946, the next in 1958, and then another in 1970. There was a gap of about 30 years before the Millennium Cohort Study was set up – so there was really very little contemporary evidence around the turn of the century on how today's children and families were faring.

The study is very multi-domain and multi-dimensional. It covers many, many different aspects of their lives. And that's really important as a research resource for many disciplines – for psychologists, economists, sociologists, epidemiologists, and health researchers. So it's broad in its scope. And that's quite a novel, useful, unique feature of it, I would say.

What are the differences between this study and previous longitudinal studies in the UK? I guess in 30 years research methods have changed, and also the factors around children's lives.

The design and setup of this study were very different. The three previous ones sampled births in a particular week. They started off being quite medically-focused, with sampling in the hospitals and NHS staff collecting data on health and development, and some basic information about the family and home.

But this was not extremely rich in terms of the family environments, at least around birth and the very early years.

So the Millennium Cohort Study (MCS) was different: it wasn't feasible, practical or desirable to run it through the NHS. It was carried out by trained interviewers who actually went out to the homes when the children were nine months old. The MCS also took a sample of births born across a period – it wasn't just one week of births. It was the first time it allowed for 'season of birth' effects to be studied at a national level. So that was an important difference, I would say, coupled with the fact that surveying was carried out by trained interviewers. What that meant is that from very early on, we could get really rich data from the parents in the home.

And then at age three, again, we continued to collect lots of detailed information about the home and family, like parenting activities, and the relationship between the parent and child in terms of the closeness, conflict or stressors and so on. We then started from a very early age to obtain measures directly from the children themselves around their development. That was quite unique to the Millennium Cohort Study, because it collected multiple measures from an early age, using state-of-the-art cognitive assessments.

Did the previous cohort studies not interview children from such an early age?

They had the birth survey. The next survey was age 7 for the 1958 cohort and age 5 for the 1970 cohort. Those early years, that 0-3 period, are just so vital for so many aspects of our lives: it's a dynamic period, and children are developing very rapidly. I believe there was a gap in our knowledge about the early years, and the MCS helps fill it by collecting measures at nine months, three and five.

The involvement of the child from a young age in MCS was really important. They were doing tests from age three. And then from age seven, they had their own questionnaires, so they could report on their lives. So that was innovative for its time – I think more and more surveys do that now.

The MCS has also asked parents about the children's socioemotional development consistently from age three to 17, which is our most recent sweep using the Strengths and Difficulties questionnaire. That's another great feature because you've got this consistent measure of another important pillar of children's development, their socioemotional and behavioural development.

The young people are coming up to age 23, you've got 21 years of data, what sorts of things are you seeing in this cohort? Anything unexpected, or different compared with previous ones?

I'll focus on children's development, which I think is a real strength of this study. There are three pillars of that.

The first is physical development. We've been measuring children's height and weight from age three, and body fat from age seven. We've certainly seen very stark increases in levels of childhood excess weight and obesity starting from quite young ages [three and five]. By age seven, we were seeing stark socioeconomic inequalities in that, and that that's quite different from the older cohorts where we didn't see those inequalities at such young ages.

We found that the results were socioeconomically graded, with children from less well-off backgrounds at much higher risk of obesity and overweight compared with those from the most advantaged families. So that's certainly something that was unexpected. I mean, we had the Jamie Oliver campaign back in the day and all of that, so we knew, maybe anecdotally, or we might have had smaller scale studies that were showing the children were more likely to be overweight in this generation compared with older generations.

But I suppose this was the first really big study across the UK that was showing this, that was evidencing it at scale using gold standard measures. It was able to track the children – showing that it wasn't improving as they were growing up – and if anything, the levels were getting worse. It was showing that between 11 and 14, there was quite an increase in obesity, suggesting that that's quite an important time for policy to focus on.

They're now entering their adult years with one in three measured as either overweight or obese. That's obviously really concerning, thinking about their future health and other outcomes.

The other area is around children's cognitive development. The cognitive assessment is from age three and importantly compares across the socioeconomic distribution. Again, worryingly, already by three, you see a clear socioeconomic gradient. So if you break down the income distribution into quintiles, what you see is at the top quintile (the richest), the children are faring much better than in the fourth quintile, the third, the second, and the first – it gets progressively worse as you move down the income distribution. That's a stark picture that couldn't be measured in the other cohorts. I think the earliest that was looked at previously was age five. So it was showing that gaps are present from a young age – and they persist. In fact, they open up if anything… the rich pull away from the poor in terms of children's development.

But it was important again to evidence and to show that, and I think that's really what New Labour was particularly interested in when it decided to ringfence a budget for this study. It wanted to understand when inequalities started to emerge, and how that varies depending on family circumstances and other factors.

The third area was emotional development. At age 14 we found that one in four females, and about one in 10 males, reported high depressive symptoms. It was the first evidence emerging from any study in over a decade, and the rates were much higher than we would have expected.

Anecdotally, we suspected that children and young people's mental health may have worsened. They were probably under a bit more pressure academically and were the first generation to grow up with social media.

However, this was the first time that we measured it using a well-validated tool at a population level. That persisted to age 17. And we've observed rising levels of self-harm.

The research drew a lot of attention to the scale of the problem that we're facing. And I think since then, there have been lots of other studies looking at it and finding a similar picture. Of course, we had Covid, which suggested it maybe got a bit worse amongst young people, and particularly females.

In terms of worsening mental health, did the results reveal any causes? Or were you only able to speculate on this?

It's very hard to do. We didn't really find that it was particularly different across the socioeconomic distribution – so it seems to affect many children, regardless of their family circumstances. Certain ethnic minorities were less likely to report high depressive symptoms compared with white children. Things like school connectedness seemed to be quite protective. But again, it's just an association. And in fact, it may be reverse causality. We did look at some associations, but certainly nothing really strong was jumping out. That's quite an active area of research to try to understand.

What we did see is that when we looked at age 17 by sexual identity, we saw sexual minority young people seemed to be at much greater risk compared with heterosexual, young people. That was quite a stark finding. And I believe that's been replicated in other studies. So it's really important to provide support, maybe to groups that are more marginalised and are still not getting the right support.

The study is multidisciplinary: how can psychologists engage and perhaps, use or learn from studies like this?

The data is openly available via the UK Data Service within about six months after they're collected. It's free for researchers to download and use for bona fide research purposes.

The study measures mental health and wellbeing at a population level, so there's lots that can be explored: psychologists can examine how it changes across the life course and how it changes for different subgroups. Because the sample size is so big, you can really look and compare different subgroups very robustly.

And then I suppose there's a lot of interest in understanding the precursors to the manifestation of later mental health and wellbeing. So there's lots that can be done there looking at the very early environment, or the environment during childhoods or when problems start to emerge. And then people can start to study why that might be. You can go into great detail if that's of interest in terms of studying mental health and wellbeing.

But then you can look at the broader the environment of the child in a holistic way, which is think is really important. You can understand how mental health relates to maybe their educational attainment, or their cognitive development, later employment, partnership formation, fertility and so on.

You did the last 'sweep' when the children were 17, and now you're going to do one at age 23 – those are key years, what are you most looking forward to finding out?

We're interested in those early adulthood transitions: from education into employment, partnership transitions and formations, and fertility and parenthood. We expect around one in 10 of the cohort to have at least one child.

There'll be a lot of interest in understanding where this generation is living, who they're living with, and whether they're renting, or if they've bought a property. And then we've lots of interest in understanding their attitudes towards things like children or the environment.

If they do have a child, quite a nice feature that we've incorporated is, they would have the option of being routed into a five-minute questionnaire which would ask them about the child and their parenting behaviours, partly to harmonise that with what their own parents would have been asked when they were very little, to study the intergenerational transmission of parenting and child development.

I'd love, as time goes on, to try to follow their children. It will be the first large-scale study that would allow for intergenerational research into how parenting and development are transmitted across generations. There are small-scale studies looking at this, particularly in psychology, but they're very low sample sizes, and not always longitudinal. This would be a valuable resource to be able to do that. So let's see.

Also, understanding their mental health and wellbeing, and how they're faring. It's post-Covid and post-Brexit - a lot has changed since we last saw them. The world has changed.

How has this study fed into the 'real world'?

The study has been influential in terms of policy in many different spheres, including children's or young people's mental health and wellbeing. To me, one of the most important things is the real-world impact that it has. That's ultimately what we're trying to do - to think of policies that can help reduce inequalities and that can help improve people's lives.

For example, there was work we did around children who experienced domestic violence in the home, on how being a witness can be very detrimental to their mental health and wellbeing. And so that then led specifically to the government adding children into the definition of victims of domestic violence. Previously it was only the person against whom the domestic violence was directed. That's important – then policies are put in place to help support all sorts of victims, so children are included in that now.

At the summer conference in London to celebrate 21 years of the 'Children of the Noughties', you met some of the actual 'children' for the first time. How did you feel that day?

Gosh! That was, for me and many others, one of the highlights of the conference. It was all very emotional. It was important to me to have them there. It was the first time we'd ever met any of the cohort members, and I just wanted them to see a room full of researchers and to feel the appreciation for everything they've contributed to the study over the years.

I felt it was important for us to acknowledge that, and I think they were also quite moved by it. It probably made them think a little bit more about the fact that their data, their voices, are being heard in all these different ways. It is feeding through to lots of research and lots of policy, and they're representing their generation. I was a bit nervous because I didn't know what to expect. But they were so lovely and charming. Honestly, they were just brilliant!

Further information

Emla Fitzsimons is Professor of Economics at University College London, and director of the UK Millennium Cohort Study, which has tracked over 19,000 children born at the turn of the millennium.

Also known as 'Child of the New Century', the study – based at the Centre for Longitudinal Studies at University College London – recently celebrated the 21 years of its participants with a conference in London

This autumn, it will start a new 'sweep' to survey the millennium children for the first time in adulthood.

Find out more about the Millennium Cohort Study