Before CHDS became CHDS

The initial inspiration for the Christchurch Health and Development Study came in the early 1970s. The primary motivating issue was the impact of single parenthood on the health and wellbeing of children. Professor Fred Shannon (see associated photo, circa 1974), who was the Foundation Professor of Paediatrics at the Christchurch School of Medicine, saw a marked increase in single parent families, who formed a disproportionate share of his clinical case load (while working as Paediatrician). Interestingly, Prof. Shannon was the first Paediatrician in Christchurch and continued as the only one until 1965. The question of what single parenthood meant for the health and wellbeing of children was one he wanted to answer rigorously, and indicative of the societal perspectives of single parent families.

To examine the health and wellbeing of children from single parent families, Prof. Shannon started a relatively small case-control study in which he intended to compare 100 children from single parent families with 100 control families. For various reasons, Prof. Shannon's initial study did not reach completion. However, by this time the New Zealand Medical Research Council (the forerunner of today's Health Research Council) had become interested in this line of research. As a consequence, the Medical Research Council invited Dr Mia Kellmer Pringle to New Zealand to provide consultation. Dr. Mia Kellmer Pringle was a child psychologist, and the founding director of the British National Children's Bureau, where she oversaw the influential National Child Development Study. Her advice was that New Zealand should invest in a longitudinal study of a birth cohort of about 1000 children to study the family, social, economic and related factors that placed children at a disadvantage. The Medical Research Council accepted the recommendation and provided preliminary funding for the study. 

In 1975, Prof. Shannon hired a young researcher named  (who would become Professor) David Fergusson, who had been working on a longitudinal study at the Ministry of Social Welfare (now known as the Ministry for Social Development), analysing a longitudinal study of 5,000 children born in 1958. That study had been aimed at documenting the antecedents of delinquency in young people. Fergusson was appointed to lead the new study, then called the Christchurch Child Development Study. By the end of 1976, a research design had been developed, funding for two years obtained, and staff appointed, including statistician (who would become Professor) John Horwood, who would remain with the Study for over 40 years. 

Ultimately the cohort that are known as our Study Members, was formed in 1977 with the recruitment of 1265 children born to mothers across all of the birthing centres in Christchurch, who gave birth between the 15th of April 1977 and the 5th of August 1977. Of the children born in Christchurch in that period, 97% were enrolled in the Study by their parents.  This remarkable participation rate was not accidental. By recruiting through the birthing centres in the city (rather than selecting families in any other way), the study ensured that babies born to people from all walks of life were included. The cohort was, from the beginning, a genuine cross-section of Christchurch society at that moment in time, and that representativeness would prove to be one of its greatest strengths in the decades of research that followed.

Data Collection in the 1970s 

Data collection in the 1970s, started at birth. In the days immediately following each child's arrival, while mothers were still in hospital, parents were interviewed by the research team. These first interviews gathered information about the family's circumstances, the mother's health, and the conditions into which the child had been born. They established the baseline from which everything that followed would be measured.

Further data collection happen when the Study Members were four months old, one year, and then every subsequent year until they turned 16 (details about further data collection are provided below). Across these early waves of data collection, information was gathered through parental interviews, health diaries kept by mothers, and hospital and general practitioner records. Parents were asked to record all of their child's medical contacts in a diary supplied by the study, which helped the research team build an accurate picture of each child's health history as it unfolded in real time rather than from memory alone.

The data gathered in these first years of the study created something of lasting value, a detailed and carefully documented starting point for each participant. By capturing the circumstances of each child's birth and the conditions of their earliest life, the CHDS made it possible to trace connections between those early experiences and outcomes that would not become visible for years or even decades. An example of this early data collection was the systematic recording of infant feeding practices during Study Members' first year of life, including whether each child was breastfed or formula-fed, and for how long. This seemingly simple piece of information would later prove significant in a series of studies examining whether and how infant feeding practices shaped children's health, cognitive development, and social adjustment in the years that followed (see the 1980s for more information on this). The 1970s data, gathered in hospital wards and family homes across Christchurch, became the foundation on which all subsequent research was built.

Context of New Zealand in the 1970s

A Country at a Crossroads

The New Zealand into which Study Members were born in 1977 was a country navigating significant uncertainty. The long postwar economic boom that had sustained full employment and relative prosperity through the 1950s and 1960s was over. The 1973 oil crisis had sent shockwaves through Western economies, and New Zealand, heavily dependent on imported oil and on preferential trade access to Britain that had been disrupted by British entry into the European Economic Community in 1973, was particularly exposed. Inflation was rising, the cost of living was increasing, and the assumptions of stability that many New Zealand families had built their lives around were beginning to feel less secure. The families who brought their babies into the world in 1977 were doing so in a country that was at times quietly anxious about what the future held.

For the CHDS, this economic context was not merely background. The study had been designed in part to understand how material disadvantage shaped children's health, wellbeing and lives, and the families enrolling their children in 1977 were living through a period in which financial pressure was becoming a more common feature of family life. The data collected in those early years would later allow researchers to examine how the economic conditions of a child's birth and infancy shaped their development in ways that only a long-term longitudinal study could reveal.

The Changing Shape of the New Zealand Family

As mentioned before, one of the central motivations for the study, visible in Professor Shannon's original clinical concern about single parenthood, was that the New Zealand family was changing. Divorce rates were beginning to rise through the 1970s, and solo parenthood was increasing and becoming more visible as a feature of New Zealand life. And while single parenthood was still relatively uncommon in the 1970s by the standards of what would follow in the 1980s and beyond, the concerns and curiosities associated with those in single parent families was growing. The social stigma attached to single parenthood remained significant and explicit in the 1970s and 1980s, and the material challenges faced solo parents, particularly solo mothers, were considerable.

The changing shape of families and single parenthood were not merely a backdrop to the study. They were in many respects its reason for existing. The original question that Professor Shannon had been trying to answer, what does growing up in a single parent family mean for a child's health and wellbeing, was embedded in the study's design from the beginning. The families who enrolled their children in the CHDS in 1977 included both two-parent and single parent households, making it possible for the first time in New Zealand to follow children from both kinds of family over time and understand what difference family structures and socioeconomic situations actually made to children's outcomes.

Women, Work, & a Shifting Society

The 1970s was also the decade in which second wave feminism arrived in New Zealand. The women's liberation movement was challenging assumptions about women's roles in the home and the workforce, and New Zealand had passed the Equal Pay Act in 1972, formally recognising for the first time that women deserved equal remuneration for equal work. The debate about what women's lives should look like, whether they should be in the paid workforce or at home raising children, whether they could and should do both, and what support they needed to do so, was live and contested throughout the decade

For the mothers of Study Members, many of whom were young women in their twenties when their children were born in 1977, these debates were not distant. They were part of the texture of daily life. The CHDS captured this moment in its data, recording information on maternal employment, family structure, and household circumstances that would later allow researchers to examine how the shifting roles of women in New Zealand society intersected with the health and development of their children.

Te Ao Māori: Land, Rights, & Our Nation Trying to Reckon with Itself

The 1970s was a decade in which the long history of Māori land loss began to demand a public answer in ways that could no longer be deferred. In 1975, two years before Study Members were born, Māori elder and activist Whina Cooper led a hīkoi of more than one thousand kilometres from Te Hapua in Northland to Parliament in Wellington, protesting the ongoing alienation of Māori land and demanding the Crown honour its obligations under Te Tiriti o Waitangi. In the same year, the Waitangi Tribunal was established, creating for the first time a formal mechanism through which Māori could bring claims against the Crown for Treaty breaches. For Māori Study Members in particular, this was the New Zealand their whānau were raising them in, one in which questions of land, justice, and Treaty rights were no longer abstract but were being contested in public and on occupied ground. The CHDS collected data on ethnicity and family background from its very first interviews, and was positioned from the beginning to document how these dynamics of disadvantage and identity shaped the lives of Māori children and their cohort across the decades that followed.

Data Collection in the 1980s

Throughout the 1980s, data collection expanded significantly as Study Members moved through early childhood and into their school years. From the age of 6, which fell in 1983, a new source was added: the class teachers of all Study Members were asked each year to complete a standardised questionnaire describing each child's behaviour at school and their academic progress. Teacher compliance was exceptionally high, with more than 95% completing the questionnaire in any given year.

When Study Members turned 8 in 1985, data collection took another significant step forward with the introduction of direct psychometric assessment. Each year from that point, Study Members were assessed individually using standardised tests of intelligence, reading ability, and mathematical ability. Structured interviews were also introduced, gathering information directly from the children themselves on topics including self-esteem and, as they grew older, early experiences with alcohol, cigarettes, and other substances.

By the time Study Members reached 11 in 1988, the study actively followed 1048 children, representing 83% of the original cohort and 92% of all cohort members still alive and resident in New Zealand. The primary source of loss was families emigrating overseas, accounting for more than half of all departures. By this point, the CHDS held over a decade of detailed, multi-source information on each participant, a record of childhood that no retrospective study could have assembled.

Operation 'Tooth Fairy'

Study Members may remember their teeth being collected for 50 cents in the early 1980s. Operation Tooth Fairy became known among parents for paying considerably more than the going rate for a lost tooth. Back in the chemistry laboratory at the University of Canterbury, those teeth were put to important use. Lead exposure could be measured in the dentine of baby teeth, allowing CHDS researchers to examine the relationship between lead exposure and the behavioural and cognitive outcomes of Study Members. In total, ten publications have focused on the outcomes of children with the highest lead levels. The findings consistently showed that children with elevated lead exposure tended to struggle more with both academic and behavioural aspects of school. A 1993 paper in the Journal of Child Psychology and Psychiatry was central to this work, and the cumulative body of CHDS research contributed to the removal of lead from petrol in New Zealand in 1996.

Breastfeeding & Child Health

When the CHDS began, one of the most widely held beliefs in paediatric medicine was that breastfeeding made a broad and pervasive contribution to children's health, reducing infection risk, protecting against eczema and asthma, and supporting cognitive development and social adjustment. The CHDS was well placed to test these claims, having collected detailed infant feeding information from birth and tracked each child's health in the years that followed.

The findings, emerging through a series of linked papers across the late 1970s and 1980s, offered only partial support for the strongest claims. When researchers accounted for the social and family factors that also shape child health, most apparent benefits of breastfeeding did not hold up under scrutiny. Two exceptions stood out: breastfed infants showed a clear reduction in minor vomiting and diarrhoea in their first four months, and there was a small but consistent tendency for breastfed children to perform somewhat better on cognitive tests in their early school years. The CHDS's contribution here was not to dismiss breastfeeding but to bring precision to a debate that had often run ahead of the evidence, clarifying what the data actually supported.

Parental Smoking & Child Health

Running alongside the research on infant feeding was a parallel programme examining the effects of parental smoking on children's health. Smoking rates in New Zealand in the late 1970s and early 1980s were high, and the mechanisms by which a parent's smoking might harm their child were only beginning to be understood.

The findings were clear and consistent. Studies examining maternal smoking during pregnancy confirmed that infants whose mothers smoked tended to be smaller at birth, with CHDS data estimating a loss of approximately 100 grams of birthweight per ten cigarettes smoked daily. Smoking mothers also had higher rates of very low birthweight infants and more frequent requirements for intensive neonatal care. Subsequent studies found that during the first two years of life, children whose parents smoked had significantly higher rates of lower respiratory illness, with maternal smoking identified as the primary driver. These findings contributed to the growing international evidence base that would eventually underpin major changes in New Zealand's public health policy around smoking in the presence of children.

Childhood Asthma

New Zealand has long had among the highest rates of childhood asthma in the world, and this was already apparent in the CHDS data. By the time Study Members reached six in 1983, 10% had made two or more medical consultations for wheezing or associated symptoms diagnosed as asthma or wheezy bronchitis.

A six-year longitudinal study examined the social, environmental, and biological factors associated with the onset of asthma during early childhood. The results were in some ways unexpected. A wide range of factors that might have been expected to play a role, including family social background, infant feeding practices, parental smoking, household pets, and family stress, were not associated with whether a child developed asthma or how severe it was. Instead, the factors that did predict early childhood asthma all pointed in a biological direction: asthma was more common in boys, in children with a family history of the condition, in those with eczema, and in children who had wheezed during infancy. This was a significant contribution to an international debate, helping focus attention on biological pathways at a time when many researchers were concentrating on environmental explanations.

What the CHDS Revealed About Children's Lives in New Zealand

The research emerging through the 1980s was building a detailed and sometimes uncomfortable picture of childhood in New Zealand. Studies examining family adversity found that while only 8% of children from low-stress families had been admitted to hospital for accidents or infections over a five-year period, nearly 40% of children from high-adversity families had been. Even after accounting for social background, the link between family stress and children's physical health and safety remained strong.

A second significant finding concerned access to services. Despite New Zealand providing free immunisation, well-child checks, preschool dental care, and early childhood education, the CHDS consistently found that the most disadvantaged children were the least likely to receive them. More affluent families were consuming a disproportionate share of public investment in child health and education. These findings echoed what was called the law of inverse care, and they contributed to policy conversations about how to better reach vulnerable children that would continue for decades.

New Zealand in the 1980s

Te Ao Māori: A Cultural Renaissance

The 1980s was a decade of profound change in how Māori identity and culture were understood and expressed. Te Kōhanga Reo, the Māori language nest movement, was established in 1982, offering whānau a way to immerse their youngest children in te reo Māori at a time when the language faced serious decline. Its rapid growth represented a wider flowering of Māori cultural confidence and political assertion. The Waitangi Tribunal, established in 1975, was gaining significant momentum, bringing questions of justice, sovereignty, and the relationship between Māori and the Crown into sustained national conversation.

For Māori Study Members, this was a decade in which the culture and language of their tūpuna were being actively reclaimed and celebrated in ways that had not been possible for their parents' generation. For all New Zealanders growing up in this period, the Māori cultural renaissance was part of the air of the decade, present in public life, in education, and in an evolving national sense of what it meant to be from Aotearoa New Zealand. The CHDS, which had collected data on the ethnicity and cultural background of Study Members from its earliest years, was positioned to document how these shifts in cultural identity intersected with health and development across the cohort.

The Springboks Tour of New Zealand, 1981

In the winter of 1981, South Africa's Springbok rugby team toured New Zealand, dividing the country in ways that spilled from political debate into the streets. On Saturday 15 August, the tour arrived in Christchurch. Six thousand protesters marched from Cathedral Square to Lancaster Park, where more than 2000 police, the largest police operation in New Zealand's history at that time, were deployed to ensure the match proceeded. Eleven people were taken to hospital, twenty-seven were arrested, and the crowd inside a stadium that held 50,000 numbered only 42,000 after public gate sales were cancelled.

The tour forced New Zealanders to confront apartheid directly, and in doing so prompted an uncomfortable reckoning with racial inequality at home. For Māori, the irony was pointed: a country condemning racial oppression abroad while dispossession of Māori land, loss of te reo Māori, and systemic disadvantage remained unaddressed. Study Members were between three and four years old during the tour, too young to remember, but they grew up in families and communities shaped by its aftermath. For those who grew up in Christchurch, 15 August 1981 was not merely history. It moved through their city and left a mark on the people and place that raised them. 

New Zealand's Economic Transformation

From 1984, New Zealand underwent one of the most rapid economic transformations of any developed country in the twentieth century. The Fourth Labour Government's programme of reform, known internationally as Rogernomics, restructured public services, deregulated markets, and reshaped the welfare state, with rising unemployment, reduced state support, and widening inequality among the consequences for ordinary families.

For many Study Members and their families, this was not an abstract economic debate but a lived reality, experienced through job losses, financial stress, and changes to the services they depended on. CHDS data collected through this period captured those circumstances in real time, providing the means to examine how economic disadvantage and household instability shaped children's development during a period of significant national disruption. 

Changing Families

The 1980s was a decade in which the shape of the New Zealand family was changing visibly. Rates of divorce and separation rose, solo parenthood became increasingly common, and the family structures into which Study Members had been born were no longer universal. These shifts were experienced by children as the departure of a parent, the arrival of a new partner, changes of home and school, and the emotional terrain of growing up in a household that looked different from the one assumed as normal.

The CHDS had been designed in part to understand exactly these dynamics. The study's original motivation was concern about the effects of solo parenthood on children's health and wellbeing, and by the 1980s researchers were publishing work on family change, parental separation, and its consequences for children's behaviour and development. This research gave New Zealand one of the most detailed longitudinal accounts anywhere in the world of how family change shapes children's lives.

Women, Work, and the Question of Childcare

The 1980s saw growing numbers of New Zealand women entering the paid workforce, including mothers of young children. This prompted significant public debate about childcare availability, the developmental effects of early day care, and the competing demands on families in which both parents worked. These were questions that touched the daily lives of Study Members and their parents directly.

The CHDS was researching these questions in real time. For many Study Members, the decade was shaped by these shifting arrangements, whether they were cared for by a parent at home, attended early childhood education, or were looked after by extended family while their parents worked.

Lead, Petrol, and the Environment Children Grew Up In

One of the less visible features of childhood in the 1980s was environmental lead exposure. Throughout the decade, leaded petrol remained in widespread use on New Zealand roads, releasing lead particulates into the air of every city and suburb. Children playing near roads or simply living in urban environments were being exposed to low levels of lead as a routine feature of daily life, without anyone fully understanding the long-term consequences. New Zealand would not complete the phase-out of leaded petrol until the 1990s.

This context gave Operation Tooth Fairy its broader significance. The CHDS was not examining an exotic contamination but something present in the everyday environment of every child in the study, and the finding that even low levels of lead exposure were associated with measurable effects on school performance raised urgent questions about a risk New Zealand had not yet fully reckoned with.

Canterbury Air Pollution in the 1980s

Christchurch's geography and its reliance on coal and wood burning for winter heating trapped pollutants close to the ground, exposing young children to elevated particulate matter throughout the 1980s. Decades later, a collaboration between the CHDS and the University of Canterbury's GeoHealth Laboratory linked longitudinal participant data with historical air pollution records. The findings showed that exposure to air pollution was not evenly distributed, with socioeconomic factors playing a significant role in determining which communities bore the greatest burden, demonstrating the enduring value of longitudinal data in addressing health questions that could not have been anticipated when the study began.

The Homosexual Law Reform Act in 1986

In 1986, New Zealand decriminalised homosexuality with the passage of the Homosexual Law Reform Act. The law was a milestone, but the debate surrounding it reflected deep stigma, and the AIDS epidemic, which had arrived in New Zealand in 1984, intensified that stigma further by associating the disease with gay men in ways that compounded existing prejudice. Study Members who would later identify as gay, bisexual, or otherwise part of LGBTQ+ communities came of age in this atmosphere. The CHDS's later research on sexual orientation and mental health reflects an understanding of how profoundly those years of stigma and legal discrimination shaped health and wellbeing across a lifetime.

The Sinking of the Rainbow Warrior in 1985

On 10 July 1985, agents of the French intelligence service bombed the Greenpeace vessel Rainbow Warrior in Auckland Harbour, killing crew member Fernando Pereira. The attack was intended to prevent Greenpeace from protesting French nuclear testing in the Pacific. New Zealand was already committed to an anti-nuclear position under Prime Minister David Lange, having banned nuclear-armed and nuclear-powered ships from its ports. The bombing transformed a principled but contested stance into something felt personally and unanimously by New Zealanders, and it contributed directly to the conditions in which the Nuclear Free Zone, Disarmament, and Arms Control Act passed in 1987. For many New Zealanders, the Rainbow Warrior and the legislation that followed stand as the moment the country declared, clearly and permanently, the kind of nation it intended to be.

Study Members were eight years old in the year of the bombing, growing up in households where opposition to nuclear weapons was not a political position so much as a deeply felt conviction. Their parents had come of age during the Cold War, shaped by French nuclear testing at Mururoa Atoll from 1966 onward and by the fear that had made nuclear catastrophe feel genuinely imminent during the Cuban Missile Crisis of 1962. It was this inheritance that gave the sinking of the Rainbow Warrior its particular emotional force for New Zealand families in 1985.

Data Collection in the 1990s

The 1990s marked a significant transition in how data was collected from Study Members. Through childhood and adolescence, the cohort had been assessed annually from birth to age sixteen, building a detailed year-by-year record of each participant's health, development, and family circumstances. As Study Members moved into adulthood, the rhythm of data collection changed. Assessments continued at ages eighteen and twenty-one, gathering information directly from Study Members themselves on the full range of their experiences as young adults.

By the time Study Members reached twenty-one years of age in 1998, the study had accumulated more than forty million characters of data describing the life histories of the cohort. The information gathered spanned prenatal and perinatal history, family social background, parental characteristics, family change and stability, exposure to abuse and family dysfunction, child health, educational achievement, behavioural adjustment at school, peer relationships, mental health and psychosocial adjustment in adolescence and young adulthood, and participation in tertiary education and the workforce. At age twenty-one, 1011 Study Members remained active in the study, representing 80% of the original cohort. Sample loss over the decade came primarily from emigration overseas, which accounted for half of all losses, followed by refusals to participate. Despite these losses, the cohort remained large enough to support research of considerable statistical power, and extensive testing consistently showed that the conclusions drawn from the data were not distorted by the pattern of who had left the study.

Adolescence & Mental Health

As Study Members moved through their teenage years in the 1990s, the CHDS was producing some of its most significant and internationally recognised research, much of it drawing directly on what Study Members and their parents had shared with the study across the preceding decade and a half of data collection.

One of the most striking findings to emerge from this period concerned the prevalence of mental health problems among adolescents. When Study Members were assessed at age fifteen, approximately one in four met the diagnostic criteria for at least one mental health disorder. By age eighteen that figure had risen to more than forty percent. Anxiety and mood disorders were significantly more common among young women, while rates of substance use disorders were higher among young men by eighteen. Despite the scale of these difficulties, less than one in four of those who met the criteria for a mental health disorder sought or received any form of treatment or assistance. The reasons Study Members gave for not seeking help were telling: many believed they did not need treatment, or that the problem would resolve on its own, or simply had not thought to seek help. These findings presented a significant challenge to New Zealand's mental health system and contributed directly to policy conversations about how young people with unmet mental health needs could be better identified and supported.

Understanding What Puts Young People at Risk

Because the CHDS had followed Study Members from birth, it could examine risk factors that predated problems by years or even a decade, a capability no retrospective study could match.
Lead levels measured in Study Members' baby teeth in the early 1980s were still associated with small but persistent deficits in educational outcomes at age 18, extending the study's contribution to the evidence base that supported the removal of lead from New Zealand petrol in 1996.

When Study Members were asked at age 18 about childhood experiences of sexual abuse, the findings were sobering. Severe childhood sexual abuse was associated with significantly increased risks of depression, anxiety, conduct problems, substance use disorders, and suicidal behaviours in young adulthood, associations that persisted after extensive efforts to account for other factors. At a time when childhood sexual abuse was only beginning to receive serious public attention in New Zealand, this provided a rigorous evidential foundation for understanding its lasting consequences.

The study also broke new ground on sexual orientation and mental health. At ages 18 and 21, 2.6% of the cohort identified as gay, lesbian, or bisexual, and this group faced odds of mental health disorder between approximately 2- to 6-times higher than heterosexual Study Members. Published in Archives of General Psychiatry in 1999, the findings provided some of the first rigorous longitudinal evidence in the world that minority sexual orientation was associated with substantially elevated mental health risks, pointing clearly to the role of stigma and social environment.

Suicidal Behaviour in Adolescence & Early Adulthood

The CHDS produced a body of work in the 1990s on suicidal behaviour that was both scientifically significant and of direct public health relevance to New Zealand, which during this period had among the highest rates of youth suicide in the developed world. The longitudinal data allowed researchers to examine the development of suicidal thoughts and attempts from adolescence into young adulthood in a way that no retrospective study could have achieved.

The findings were confronting. By the age of 21, more than one quarter of Study Members reported having experienced suicidal thoughts, and nearly eight percent had made a suicide attempt. Analysis of the factors associated with these outcomes pointed to a life course model in which risk accumulated across multiple domains: adverse childhood circumstances, personality characteristics, the development of mental disorders, and exposure to stressful life events. Of these factors, the development of a mental disorder, particularly a mood disorder, made the strongest independent contribution to suicidal risk. This work contributed directly to the development of practical guidance for New Zealand schools and health services on identifying and supporting young people at risk of suicide.

Cannabis, Substance Use, & Adolescent Risk

The 1990s was also the decade in which Study Members were navigating the risks associated with substance use as teenagers and young adults. The CHDS gathered data directly from Study Members on their use of alcohol, cannabis, and other substances, and researchers used this information to examine the consequences of early onset use for later personal adjustment.
The cannabis research in particular attracted considerable attention. The CHDS produced a series of papers in this decade examining the associations between early cannabis use and later outcomes, finding that early and regular use was associated with increased risks of a range of adverse outcomes including educational underachievement and the use of other illicit substances. This body of work was directly relevant to New Zealand public policy and was referenced in submissions to the Parliamentary Select Committee on Health's inquiry into the mental health effects of cannabis. The study's contribution to that inquiry was one of a number of instances in the 1990s where CHDS research moved directly from the academic literature into the policy domain.

From Evidence to Action: The Birth of Early Start

One of the most tangible outcomes of CHDS research in the 1990s was not a paper but a programme. Research had shown that young people reared in the most disadvantaged five percent of the cohort had risks of severe behavioural and adjustment problems more than one hundred times those in the most advantaged half. The implication was clear: meaningful progress required intervening much earlier, before disadvantage had already shaped a child's trajectory. 

This finding directly drove the development of Early Start. From 1995, a Christchurch consortium including the CHDS, the Family Help Trust, Plunket, Pegasus Health, the Department of Child, Youth and Family Services, and Māori community representatives developed a home-based family support programme for high-risk families from the birth of their child. A randomised controlled trial comparing 220 Early Start families with 223 control families found that Early Start children had improved health outcomes, greater exposure to early childhood education, more positive parenting, and significantly lower rates of severe physical assault by parents. The programme performed favourably against the best home visitation programmes internationally and remains operating in Christchurch today.

New Zealand in the 1990s

The Mother of All Budgets & Cost of Reform

The economic reforms of the 1980s had reshaped New Zealand's economy, but their full social consequences became most visible in the early 1990s. In 1991, Finance Minister Ruth Richardson delivered what became known as the Mother of All Budgets, a package of cuts to welfare benefits, housing subsidies, and public services that significantly reduced the safety net for the country's most vulnerable families. Unemployment reached levels not seen since the Great Depression. Child poverty deepened measurably across the early years of the decade.

For Study Members, who were teenagers during this period, these conditions formed the economic backdrop to their adolescence. For their families, many of whom had already been under financial pressure through the late 1980s, the early 1990s brought additional hardship. The CHDS data collected through this period captured the material circumstances of families in real time, and the study's research on the consequences of socioeconomic disadvantage for adolescent mental health, substance use, and educational outcomes drew directly on experiences of the families in the cohort during these difficult years.

The Health System Restructuring

Alongside the economic reforms, the 1990s saw a fundamental restructuring of New Zealand's health system. Regional health authorities replaced area health boards, public hospitals became Crown Health Enterprises operating on commercial principles, and the relationship between the state and the delivery of health care was recast in ways that proved deeply controversial. Mental health services, which the CHDS research was revealing to be dramatically underutilised by young people in need, were reorganised repeatedly across the decade amid ongoing debate about funding, access, and quality.

For Study Members navigating the mental health system as teenagers or young adults, these structural changes shaped what services were available and how easy or difficult it was to access them. The CHDS finding that fewer than one in four young people who met the criteria for a mental health disorder received any form of treatment was produced in this context, and it was partly a reflection of a system that was struggling to reach the young people who needed it most.

The Internet & a Changing World

The 1990s was the decade in which the internet arrived in New Zealand homes and began to reshape how people communicated, accessed information, and understood their place in the world. Study Members were among the first generation to navigate adolescence alongside this technology, and by the late 1990s email, early social platforms, and the World Wide Web were becoming features of daily life for many young New Zealanders. The long-term consequences of this shift for social development, mental health, and wellbeing would not become visible for years, but the CHDS was positioned to examine them as they unfolded into the following decade.

Data Collection in the 2000s

As Study Members moved through their twenties and into their thirties, data collection continued at two significant points during the decade. Study Members were assessed at age twenty-five, in approximately 2002, and again at age thirty, in approximately 2007. These data collection waves marked an important transition in the nature of the study. For the first time, researchers were examining Study Members not primarily as children or adolescents but as adults with their own partnerships, careers, households, and in many cases their own children. The information gathered at these waves built directly on the preceding twenty-five years of longitudinal data, making it possible to trace connections between the circumstances of a person's childhood and birth and the shape of their adult life in ways that no other study design could achieve.

Cannabis, Mental Health, & a National Debate

One of the most significant and internationally visible CHDS research contributions of the 2000s concerned the relationship between cannabis use and mental health, particularly psychosis. Through the 1990s, the study had documented patterns of cannabis use among Study Members and their associations with a range of adverse outcomes. In the 2000s, researchers were able to examine whether those associations reflected a genuine causal effect of cannabis on mental health outcomes, or whether they were explained by pre-existing vulnerabilities that led people both to use cannabis and to develop mental health problems.

The findings contributed to a substantial and contested international literature on cannabis and psychosis. CHDS research in this area provided longitudinal evidence that early and regular cannabis use was associated with elevated risks of psychotic symptoms and other mental health difficulties, even after accounting for pre-existing psychiatric vulnerability. This was research with direct policy relevance in a decade when the legal status of cannabis was under active debate in New Zealand and internationally, and CHDS findings were cited in that debate.

Growing Up: Study Members as Adults

The 2000s was the first decade in which the CHDS was able to examine its Study Members as fully formed adults. Research in this period looked at the long-term consequences of childhood experiences on adult outcomes across a wide range of domains including partnership stability, parenting, employment, mental health, and physical health. A recurring and important finding across many of these research streams was that childhood adversity cast a long shadow. The disadvantages and difficulties that CHDS researchers had documented in the families of Study Members in the 1970s and 1980s were visible in the outcomes of those Study Members in their twenties and thirties, even after accounting for many other influences.

This was also the period in which the study began examining Study Members' own experiences of parenthood, creating for the first time the possibility of examining intergenerational patterns. Study Members who had grown up in difficult or disadvantaged circumstances were beginning to form their own families, and researchers were interested in understanding how those early experiences shaped the kind of parents Study Members became and the environments their own children were growing up in.

Physical Punishment and the Anti-Smacking Legislation

Throughout the early 2000s, New Zealand society was engaged in a sustained and at times deeply divisive debate about the use of physical punishment by parents. The debate centred on Section 59 of the Crimes Act, which had long provided parents with a defence of "reasonable force" in cases of physical punishment. Advocates for reform argued that this provision effectively permitted child abuse under another name, while opponents of change argued that it criminalised ordinary parenting and represented an unacceptable intrusion by the state into family life. 

CHDS data made an important contribution to this debate. The cohort had been providing information about parenting practices and physical punishment since the study's earliest years, and those data spoke directly to questions about how common physical punishment was, how it was associated with child outcomes, and what the evidence suggested about its effects. When the Crimes Amendment Act was passed in 2007, removing the reasonable force defence, it was the culmination of a debate in which research evidence, including evidence from the CHDS, had played a significant role.

A paper published by CHDS researchers in 2021, drawing on data collected between 2002 and 2017, examined what had changed in the years since the legislation came into effect. The findings were sobering. Despite the legal change, physical punishment remained a common form of discipline among parents in the study period, indicating that legislation alone had not been sufficient to change deeply embedded parenting practices. The research also documented that 96.3% of Study Members themselves had experienced some form of parental physical punishment during their own childhoods, providing a striking illustration of how normalised physical punishment had been in the generation raised in the 1970s and 1980s.

New Zealand in the 2000s

11 September 2001 and New Zealand's Place in the World

The attacks of 11 September 2001 in the United States sent shockwaves through every country with connections to the Western world, and New Zealand was no exception. The events of that day reshaped international politics, security, and travel in ways that affected the daily lives of people far beyond American borders. New Zealand contributed personnel to international operations in the aftermath of the attacks, and the decade that followed was shaped by the ongoing consequences of a global shift in how nations understood security, terrorism, and international obligation.

For Study Members, who were in their mid-twenties when the attacks occurred, September 11 arrived at a moment in adult life when many were establishing careers, forming relationships, and beginning to engage with the world beyond New Zealand's shores as travellers, workers, and citizens. The memorial gifted to Christchurch by New York City in honour of the firefighters who died that day stands as a reminder of the city's connection to those events and to the global grief they produced.

The Foreshore and Seabed, & Māori Political Assertion

In 2004, the New Zealand Government passed the Foreshore and Seabed Act, extinguishing Māori customary title to the foreshore and seabed and vesting it in the Crown. The legislation provoked the largest Māori protest march in New Zealand's history, with tens of thousands marching to Parliament in Wellington. It also precipitated a political realignment, with Tariana Turia resigning from the Labour Government to found the Māori Party, which went on to win seats in the 2005 election and establish itself as an independent Māori voice in Parliament.

For Māori Study Members, the Foreshore and Seabed controversy was part of a broader pattern of political engagement and assertion that characterised the decade. The continuing work of the Waitangi Tribunal, the growing presence of Māori political representation in Parliament, and the ongoing debates about Treaty obligations and indigenous rights were part of the political landscape in which they were building their adult lives. The CHDS, which had collected data on ethnicity and cultural identity from the study's earliest years, held information that was increasingly relevant to understanding how these political and social dynamics intersected with health and wellbeing outcomes for Māori New Zealanders.

The Civil Unions Act in 2004

In 2004, New Zealand passed the Civil Unions Act, creating a legal framework for the recognition of same-sex partnerships. The legislation was significant for LGBTQ+ New Zealanders, arriving seventeen years after homosexuality had been decriminalised and at a time when the social acceptance of gay and lesbian identity had shifted considerably from the fear and stigma of the 1980s. For Study Members who identified as gay, lesbian, or bisexual, and whose mental health had been shown by CHDS research to be significantly affected by growing up in an environment of stigma and legal discrimination, the Civil Unions Act was a meaningful if incomplete step toward fuller recognition.

The CHDS had published its research on sexual orientation and mental health in 1999, providing some of the first rigorous longitudinal evidence that minority sexual orientation was associated with substantially elevated mental health risks. In the decade that followed, the social and legal environment for LGBTQ+ New Zealanders was changing, and the question of how those changes affected wellbeing outcomes was one the study was positioned to examine.

The Global Financial Crisis & New Zealand Families

The global financial crisis that erupted in 2008 brought the longest period of economic growth New Zealand had experienced to an abrupt end. While New Zealand's banking system was more insulated than some, the consequences were felt in employment, household incomes, and the availability of credit. For Study Members who were in their early thirties in 2008, many with mortgages, young children, and careers that had been built during the preceding period of growth, the financial crisis arrived at a moment of significant personal exposure and responsibility. The economic pressures of the late 2000s would shape the circumstances of a new generation of New Zealand children, the children of Study Members, in ways that echoed the findings of CHDS research about the consequences of economic disadvantage for child development.

Data Collection in the 2010s

The 2010s saw two significant data collection waves for the CHDS cohort. Study Members were assessed at age 35, in approximately 2012, and again at age 40, in approximately 2017. By this point in the study's life, researchers were examining Study Members as middle-aged adults with established adult identities, many with children of their own approaching or entering adolescence. The questions being asked had evolved considerably from those of the early waves. Alongside continuing measures of mental health, substance use, and socioeconomic circumstances, the study was examining adult health, relationships, employment, and the long-term consequences of experiences that in some cases dated back to the very beginning of the cohort's life.

The Canterbury earthquakes created an additional and unplanned data collection opportunity, with the study gathering information specifically about Study Members' experiences of the disaster and its aftermath. This information, combined with the existing longitudinal record, placed the CHDS in a uniquely powerful position to understand the health consequences of major natural disaster exposure in a well-characterised adult population.

The Canterbury Earthquakes & CHDS Research

On 4 September 2010, a magnitude 7.1 earthquake struck Canterbury shortly before dawn. The city escaped without fatalities, but the damage was extensive and the aftershock sequence that followed was relentless. Then, on 22 February 2011, a magnitude 6.3 earthquake struck at lunchtime on a working day, collapsing buildings across the central city and killing 185 people. It remains New Zealand's second deadliest natural disaster. Thousands of aftershocks continued across the following years, and the rebuilding of central Christchurch became one of the defining projects of the decade.

Approximately half of the CHDS cohort were living in the Canterbury region when the earthquakes struck, meaning the study held pre-existing longitudinal data on a large group of people who had just experienced a major natural disaster. This placed the CHDS in a position that virtually no other longitudinal study in the world could match: the ability to examine how earthquake exposure affected the health and wellbeing of a well-characterised population whose pre-disaster circumstances were already thoroughly documented.

CHDS researchers sought to understand the health impact among Study Members who had experienced the earthquakes compared with those who had not. Research findings examined the psychological impacts of the disaster including rates of post-traumatic stress, depression, and anxiety, as well as physical health outcomes including a finding of a correlation between experiencing a major natural disaster and changes in body weight. The longitudinal design made it possible to distinguish between outcomes that were genuinely attributable to earthquake exposure and those that reflected pre-existing vulnerabilities or circumstances, a distinction that simpler study designs could not make with confidence.

Sexual Orientation, Identity, and the Legalisation of Same-Sex Marriage

In April 2013, New Zealand became the first country in the Asia-Pacific region to legalise same-sex marriage, with the Marriage Amendment Act passing Parliament to widespread celebration. For LGBTQ+ Study Members, many of whom had grown up in the shadow of the stigma and fear documented in CHDS research from the 1990s and 2000s, this was a significant and personal milestone.

CHDS research in this decade continued to examine the relationship between sexual orientation, identity, and mental health outcomes across the cohort. A study drawing on data from Study Members explored the diversity of sexual identities within the cohort and examined how these identities related to mental health outcomes across the life course. This research found that while the majority of Study Members reported a heterosexual identity, a significant minority identified as part of sexual minority groups, and that mental health disparities between heterosexual and sexual minority cohort members remained an important and ongoing concern.

The Christchurch Mosque Attack on the 15th of March 2019

On the 15th of March 2019, a terrorist attack on two mosques in Christchurch during Friday prayers killed fifty-one people and injured many more. It was the deadliest act of mass violence in New Zealand's modern history, and its impact on Christchurch and on the country was profound. New Zealand's swift legislative response, with semi-automatic weapons banned within weeks of the attack, was widely praised internationally as a model of decisive action in the face of gun violence. 

For Study Members living in Christchurch, the attack arrived in a city that was still rebuilding from the earthquakes of 2010 and 2011, adding a new layer of trauma to a community that had already endured a great deal. The attack and its aftermath reinforced conversations about belonging, identity, racism, and the obligations of communities toward those within them who face discrimination and violence. New Zealand Prime Minister Jacinda Ardern's response, including her immediate and public embrace of the Muslim community and her refusal to name the perpetrator publicly, became internationally recognised as an example of compassionate and principled leadership in crisis.

New Zealand in the 2010s

Rebuilding Christchurch

The years following the 2011 earthquake saw Christchurch undertake one of the most significant urban rebuild projects in New Zealand's history. The central city was effectively demolished and reimagined, with new architectural approaches, the famous cardboard cathedral, and significant debate about the pace, direction, and inclusivity of the rebuild process. For Study Members living in Christchurch, the decade was shaped by the physical and emotional experience of watching their city change, navigating the ongoing aftershocks, the insurance claims, the red-zoning of residential land, and the gradual, uneven return of normality.

Social Progress and Ongoing Inequalities

Alongside the Marriage Amendment Act of 2013, the 2010s brought other significant social changes to New Zealand. The Child Poverty Reduction Act of 2018 introduced statutory requirements for the government to measure and report on child poverty, an acknowledgement that poverty remained a serious and persistent problem in a wealthy country. For the CHDS, which had been documenting the consequences of childhood poverty and disadvantage since the 1970s, this legislative development represented a belated formal recognition of what the study's research had been demonstrating for decades.

Preparing for the Next Wave

As the 2020s began, the CHDS was approaching its fiftieth year of continuous data collection. The study had by this point produced hundreds of peer-reviewed publications and had contributed to policy changes and public health interventions across New Zealand and internationally. Planning was underway for a major data collection wave to coincide with Study Members' fiftieth birthdays in 2027, which would make the CHDS one of the very few longitudinal birth cohort studies in the world to have followed the same group of people from birth to the age of fifty.

The 2020s data collection wave offers a unique opportunity to examine the health and wellbeing of Study Members in midlife, including physical health conditions that become more prevalent in the late forties, mental health across the life course, the health of Study Members' own children, and the long-term consequences of everything the study has documented from the beginning. Reconnecting with Study Members who have been out of contact with the study is one of the priorities of this preparation period, and the CHDS website and this timeline are part of that effort.

Cannabis Research & the 2020 Referendum

On 17 October 2020, New Zealanders voted in a non-binding referendum on whether to legalise recreational cannabis. The referendum was ultimately defeated, with 53.4% voting against legalisation. In the period leading up to the vote, CHDS researchers contributed to the public information available to New Zealanders making their decision, drawing on decades of longitudinal data on cannabis use and its consequences. 

The research drew on data from both the Christchurch and Dunedin birth cohorts, two of the world's most significant longitudinal studies, to provide a picture of how cannabis use affected health and wellbeing over a long period of time. The findings indicated that the risks of cannabis are not uniform across the population. The greatest concentration of harm was found among those who began using cannabis at a young age and continued to use it regularly into adulthood, a pattern associated with significantly elevated risks for mental health, educational achievement, and other outcomes. For those who used cannabis less regularly or began in adulthood, the risks appeared substantially lower.