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The Dunedin Study: Nature v. Nurture Across 40 Years
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December 28, 2014, 07:42 PM
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Whenever I read denunciations of The Bell Curve, I’m struck by how little subsequent data are cited. We hear a lot of a priori arguments that were musty when the late Stephen Jay Gould was trumpeting and a lot of ad hominem anger, but few references to new data that has emerged in the 20 years since.

It’s not as if there isn’t a lot more data today.

What made The Bell Curve of particular importance was that around 1990 Murray and Herrnstein got their hands on a particularly rich data set: the federal 1979 National Longitudinal Study of Youth tracking of 12,000+ nationally representative youngish people combined with the Pentagon’s 1980 administration of the AFQT/ASVAB enlistment test to the NLSY sample.

This was due to the Pentagon’s 1976 misnorming of AFQT scores that led to the Stripes Era of the Carter Administration military.

Non-commissioned officers kept calling up Senator Sam Nunn to tell him that there must be something wrong with the new test because a lot of the new recruits were dumb as a box of rocks. Nunn finally got the brass to look into this and, sure enough, they’d screwed up in determining the passing scores.

Fortunately, there was a nationally representative sample of 15 to 23 year olds already under steam in the NLSY and adding a good cognitive test like the AFQT to it would be of benefit to social scientists as well. So in 1980 most of the NLSY panel sat down and took the AFQT so the Pentagon would finally know how smart the average American youth was. This led to the Top Gun era of the Reagan Administration military. (I’m oversimplifying history, but the misnorming fiasco deserves to be better known.)

So, if Herrnstein and Murray are wrong, we now have 20 more years of data from the NLSY79 tracking, which now includes thousands of children of females in the original study, including both mother and child IQ-like scores. You can access NLSY79 data here. The most recent published update is from 2012.

Plus we have the NLSY97 tracking study from 18 years later that has now been running for 17 years.

And we have lots of other long-term tracking samples, such as ADD Health.

Overseas, there is the Dunedin sample. The medical and dental school in the New Zealand city of Dunedin enrolled virtually every child born in Dunedin over a 12-month period in 1972-73 into this lifelong study. The subjects are now in their early 40s and their children are being enrolled as they reach age 15. A sizable documentary is being prepared on the results called “The Science of Us.” (Above is a brief trailer.)

Here are some selected papers published based on this universe of roughly 1000 individuals. (You can get the links to the papers here.)

Credit Scores, Cardiovascular Disease Risk and Human Capital

Is Chronic Asthma Associated with Shorter Leukocyte Telomere Length at Midlife?

Employment among schoolchildren and its associations with adult substance use, psychological wellbeing, and academic achievement

Community water fluoridation and intelligence: Prospective Study in New Zealand

Smoking Cessation and Subsequent Weight Change

Tobacco Smoking in Adolescence Predicts Maladaptive Coping Styles in Adulthood

Is Obesity Associated With a Decline in Intelligence Quotient During the First Half of the Life Course?

The p Factor: One general psychopathology factor in the structure of psychiatric disorders?

Prospective developmental subtypes of alcohol dependence from age 18 to 32 years: Implications for nosology, etiology, and intervention

Retinal vessel caliber and lifelong neuropsychological functioning: Retinal imaging as an investigative tool for cognitive epidemiology

Stability and change in same-sex attraction, experience, and identity by sex and age in a New Zealand Birth Cohort

Childhood and adolescent television viewing and antisocial behavior in early adulthood

The relationship between multiple sex partners and anxiety, depression, and substance dependence disorders: a cohort study

A 32-Year Longitudinal Study of Child and Adolescent Pathways to Well-Being in Adulthood

Persistent Cannabis Users Show Neuropsychological Decline from Childhood to Midlife

Does Being an Older Parent Attenuate the Intergenerational Transmission of Parenting?

Undercontrolled temperament at age 3 predicts disordered gambling at age 32: a longitudinal study of a complete birth cohort

Can Childhood Factors Predict Workplace Deviance?

Patterns of sexual partnering and reproductive history: Associations with timing of first birth in a birth cohort

Risk factors prospectively associated with adult obsessive-compulsive symptom dimensions and obsessive-compulsive disorder

Adolescent, and their parents, attitudes towards graduated driver licensing and subsequent risky driving and crashes in young adulthood

A gradient of childhood self-control predicts health, wealth, and public safety

The Dunedin Multidisciplinary Health and Development Study: tips and traps from a 40-year longitudinal study

Consistency and reliability of self-reported lifetime number of heterosexual partners by gender and age in a cohort study

Adolescent screen-time and attachment to parents and peers

How common are common mental disorders? Evidence that lifetime prevalence rates are doubled by prospective versus retrospective ascertainment

Adverse childhood experiences and adult risk factors for age-related disease: depression, inflammation, and clustering of metabolic risk markers

Researching genetic versus nongenetic determinants of disease: A comparison and proposed unification

Predictive value of family history on severity of illness: the case for depression, anxiety, alcohol dependence, and drug dependence

And here’s the home page of psychologists Avshalom Caspi and Terrie Moffitt who have written some of the most ambitious papers based on the Dunedin population.

At James Thompson’s Psychological Comments, he summarizes an upcoming Caspi and Moffitt paper based on 40 years of Dunedin data where they look at who are net contributors and who are net consumers of the common weal.

This strikes me as potentially hugely useful in immigration policy. My opinion has been that our immigration system ought to try to exclude individuals (and thus their descendants) who are likely to cost far more than they pay in taxes. Here’s an upcoming study of a first world city over the last 40 years. (In the following block quote, Thompson's comments are in roman, the original paper in italics).

Are you a nuisance?

What if we were to take an objective measure? Track a thousand newborns, and keep a close account of the profit and loss ledger. At this point you may feel a trifle uneasy. Who are we to judge these matters? What price the jocular remark of a mute inglorious Milton? How could one possibly assess the wit of someone who lacks a Twitter account?

Furthermore, you may recoil at the possible results of such an enquiry. If some individuals turn out to be a nuisance and a high cost to society, what then? Should they be exiled to some other land whether the natives are even more generous and gullible, or should we intervene as best we can to make them into productive citizens?

The usual strategy of successful institutions these days, such as Harvard University or the New England Patriots, is to devote much care to whom they select.
These are not trivial matters, and the researchers were at pains to highlight the moral choices which arise from a clear headed evaluation of costs and benefits. In particular, their discussion pre-supposes a compassionate society, with redistributive taxation providing educational, health and welfare benefits. The question barely arises outside a welfare states. In such less kindly states, if people are a nuisance they are simply a nuisance, but not a direct cost, since no one will be paying them any benefits.

Terrie E. Moffitt & Avshalom Caspi used the ISIR 2014 conference to test reactions from assembled researchers about the findings so far, and about the issues which arise from them. They presented their data on the Dunedin study, a four-decade longitudinal study of a birth cohort of 1000 New Zealanders. They examined risk factors in childhood and measures of social, health, and economic costs in adulthood.

Adult social and economic outcomes fit the Pareto principle: 20% of the cohort accounted for approximately 80% of every outcome: the cohort’s months of social welfare benefits, years of absent-father childrearing, pack-years of cigarette smoking, hospital admissions, pharmacy prescription fills, criminal court convictions, and injury-related insurance claims. Moreover, high-cost individuals with one problem outcome tended to also have multiple problem outcomes. An ultra-high-cost sub-segment of the cohort was identified who accounted for 80% of multiple problems. …

The authors know all this, and realise that the beguiling Pareto observation is a post-hoc description, which of itself predicts nothing. In this case it simply asserts: there are some troublesome people, and they will account for most social problems. The critical question is: which kids will grow up to be responsible for a disproportionate amount of trouble (and can anything be done to make them behave better)?

The authors say: Risk factors measured in childhood that characterized this ultra-high-cost group were: low family socio-economic status, child maltreatment, low self-control, and low IQ. Effect sizes were very large. Predictive analyses showed that together, SES, maltreatment, self-control, and IQ measured in the first decade of life were able to predict 80% of the individuals who are using 80% of multiple costly services. We developed an index of the integrity of a child’s brain at age three years. This age-3 brain-integrity index was a strong predictor of the cohort members who four decades later became members of the ultra-high-cost population segment.

Implications: Much research has shown that childhood risk ‘X’ can predict poor adult outcome ‘Y’, but modest effect sizes discourage translation of findings into targeted childhood interventions. This study illustrates that the vast bulk of a nation’s social services, crime control, and health-care are expended on a relatively small population segment. During early childhood, this population segment is characterized by a small set of risk factors: low SES, child maltreatment, low self-control, low IQ, and poor brain integrity. Reducing these factors may bring surprisingly good return on investment.

The comments from the audience were that it would be an error to describe the neurological examination as an “index of the integrity of the child’s brain”. Brains are assumed to be present. Better to say that an examination of behaviour, skills and neurological responses shows that many of the troublesome children can be detected at that age.

The assessment is interesting. It includes the Peabody Picture Vocabulary Test, which is simple and a good predictor. A word is spoken and the child has only to point to the one of four pictures which best describes the word. It has been doing good work since 1959 and is an excellent example of the power of intelligence measures: simple to do but profound in their implications. …

The core of the argument is a social one, and goes to the heart of policy making. The authors calculate that about 45% of the population are “low cost users”. In other words, they draw very little on community resources, yet pay most of the taxes that provide those services to others. The authors have identified some ultra high cost users who are a net drain on resources.

When you find yourself in a hole, stop digging. Taking care of your own citizenry’s problem people is one thing, taking care of other peoples’ is something else.