Ian J. Deary

Introduction

Ian John Deary OBE (born 17 May 1954) is a Scottish psychologist who is also a qualified physician and psychiatrist. He is Professor of Differential Psychology at the University of Edinburgh, former Director of the Centre for Cognitive Ageing and Cognitive Epidemiology, and the architect of a research programme that established a fact most people find counter-intuitive: how well you score on an intelligence test at age eleven predicts how long you live.

Deary named that line of work cognitive epidemiology — the use of cognitive ability test scores as risk factors for health and mortality — and then spent two decades supplying most of its data. He also directs the Lothian Birth Cohort studies, which follow Scottish men and women whose intelligence was tested in childhood in 1932 or 1947 and who were brought back into the laboratory in old age to be tested again, scanned, genotyped, and followed until death. It is one of the few places in psychology where a question can be asked with a sixty-eight-year follow-up.

The field he founded is also one of the most contested in psychology, and Deary's own reviews have been scrupulous about the parts that are not yet settled.

Early Life and Education

Deary's route into psychology was unusually indirect. He left school and trained as a medical laboratory scientist, taking an Ordinary National Certificate in Medical Laboratory Sciences at David Dale College, Glasgow, in 1974, and a Higher National Certificate in Blood Transfusion and Haematology at Glasgow College of Technology in 1976.

He then read psychology as part of a medical sciences degree at the University of Edinburgh, graduating BSc (Medical Sciences) with first-class honours in 1980, and completed the MBChB in 1983. He practised psychiatry in London and Edinburgh and took the MRCPsych in 1991 before moving into academic psychology. His PhD was awarded by Edinburgh in 1992 for work on auditory inspection time and intelligence, supervised by the psychometrician Chris Brand — a figure whose later writings on race and intelligence led to his dismissal from Edinburgh in 1997 for gross misconduct, and whose career became an international cause célèbre over academic freedom.

The double training shows in the work. Deary's research questions are epidemiological — who dies, of what, and why — while his measurement instruments are psychometric. He is one of the few intelligence researchers who is also a Fellow of the Royal College of Physicians of Edinburgh.

Academic and Professional Career

Deary has spent his career at the University of Edinburgh, where he holds the chair in differential psychology. He founded and directed the Centre for Cognitive Ageing and Cognitive Epidemiology, a major Medical Research Council-funded centre, and has served as co-director of the Alzheimer Scotland Dementia Research Centre.

He is a past president of the International Society for the Study of Individual Differences. His early work belonged to the Edinburgh tradition of reductionist psychometrics: measurement of elementary cognitive tasks — reaction time, inspection time, and the variability of both — as correlates of general intelligence, on the argument that a general factor must be visible somewhere in the nervous system and that its simplest expressions are the place to look.

From around 2000 his work shifted decisively toward epidemiology and longitudinal cohort design. The Lothian Birth Cohorts, which he co-founded, are jointly funded by Age UK, the Medical Research Council, the US National Institutes of Health, and the University of Edinburgh.

He holds fellowships of the Royal College of Physicians of Edinburgh, the Royal Society of Edinburgh, the British Academy, the Academy of Medical Sciences, the Royal College of Psychiatrists, and the Association for Psychological Science. He held a Royal Society-Wolfson Research Merit Award from 2003 to 2007, received the first of Edinburgh's Chancellor's Awards in 2003, was named Distinguished European Personality Psychologist by the European Association of Personality Psychology in 2010, received the Lifetime Achievement Award of the International Society for Intelligence Research in 2014 and the James McKeen Cattell Fellow Award of the Association for Psychological Science in 2015. He was appointed OBE in the 2019 New Year Honours for services to the social sciences.

Major Contributions to Psychology

Cognitive Epidemiology

In 2010, writing with G. David Batty, Deary defined cognitive epidemiology as "the use of cognitive ability test scores as risk factors for human health and disease outcomes, including mortality." The field rests on a robust and repeatedly replicated association: across dozens of cohorts in many countries, higher scores on intelligence tests taken in childhood or early adulthood predict lower all-cause mortality decades later.

A meta-analysis of sixteen longitudinal studies by Catherine Calvin and colleagues, published in 2011, put the size of the effect at roughly a 24% reduction in the risk of death for each one-standard-deviation advantage in intelligence, across follow-ups of between seventeen and sixty-nine years. The association is broad rather than specific — it covers cardiovascular disease, most cancers, accidents, suicide, and homicide — which is itself an important clue: a risk factor that predicts everything is not behaving like an ordinary disease exposure.

Deary and Batty's own contribution was to insist, from the outset, that the association does not simply reduce to social class. Adjusting for childhood socioeconomic status attenuates the intelligence–mortality association very little; adjusting for the person's own adult education and occupation attenuates it substantially, in some studies entirely. Deary's response has been to argue that this second adjustment is at least partly an overadjustment — that education is so highly correlated with intelligence that controlling for it removes the variable of interest along with the confounder — while acknowledging in print that the reverse reading is equally available: that intelligence launches people into safer environments, and it is the environments that do the protecting.

The Lothian Birth Cohort Studies

The design is one of the most economical in longitudinal science. On a single day in 1932, and again in 1947, almost every child of the relevant age attending school in Scotland sat the same Moray House intelligence test. Those test booklets survived. Beginning in 2000, Deary and his colleagues traced surviving members of the 1921 and 1936 birth cohorts living in Edinburgh and the Lothians, and invited them back to retake essentially the same test — the 1921 cohort at about age 79, the 1936 cohort at about age 70 — together with extensive batteries of cognitive, biomedical, genetic, and brain-imaging measures.

Three findings stand out. Intelligence measured at age 11 correlates about r = .66 with intelligence measured at age 79 — a stability coefficient over a gap of nearly seven decades that has few equivalents in psychology. The genetic correlation between childhood and old-age intelligence has been estimated at about .62, suggesting that a single set of genetic influences is largely responsible at both ends of life. And higher childhood intelligence predicts lower mortality in old age, replicating the wider cognitive epidemiology literature within a single, unusually well-characterised sample.

The cohorts have since become a general-purpose resource for the biology of cognitive ageing: their data have been used for genome-wide association studies, DNA methylation work, brain imaging, and — in papers still appearing — investigations of everything from sedentary behaviour to gardening.

Intelligence and Elementary Cognitive Tasks

Deary's experimental work pursued the reductionist question behind the epidemiology: what is the thing that intelligence tests measure? His studies of reaction time and inspection time — the latter being how long a stimulus must be presented before a person can reliably report which of two alternatives it was — established these as reliable, if modest, correlates of psychometric intelligence, with inspection time correlations generally reported around r = .4. The programme is a direct continuation of the Edinburgh tradition associated with Hans Eysenck and, before him, Charles Spearman's argument for a general factor.

Personality, and Medically Unexplained Symptoms

Alongside the intelligence work, Deary has published extensively on personality traits — most visibly through the widely used textbook Personality Traits, written with Gerald Matthews and Martha Whiteman — and on medically unexplained symptoms, an area where his dual training as a physician and a differential psychologist proved directly useful.

Major Publications

Deary, I. J. (2000). Looking Down on Human Intelligence: From Psychometrics to the Brain. Oxford: Oxford University Press.
Deary, I. J. (2001). Intelligence: A Very Short Introduction. Oxford: Oxford University Press.
Matthews, G., Deary, I. J. & Whiteman, M. C. (2003; 3rd ed. 2009). Personality Traits. Cambridge: Cambridge University Press.
Deary, I. J., Whalley, L. J. & Starr, J. M. (2009). A Lifetime of Intelligence. Washington, DC: American Psychological Association.
Deary, I. J., Penke, L. & Johnson, W. (2010). "The neuroscience of human intelligence differences." Nature Reviews Neuroscience, 11(3), 201–211.
Deary, I. J. (2012). "Intelligence." Annual Review of Psychology, 63, 453–482.
Deary, I. J. & Johnson, W. (2010). "Intelligence and education: causal perceptions drive analytic processes and therefore conclusions." International Journal of Epidemiology, 39(5), 1362–1369.

Impact and Legacy

Cognitive epidemiology is now a recognised sub-discipline with its own literature, its own methods, and a substantial public health literature downstream of it. Deary's cohorts have become a shared international resource, and his insistence that intelligence test scores can be treated as epidemiological risk factors — alongside blood pressure or smoking — has changed what questions intelligence researchers ask. His students and collaborators now hold posts across cognitive ageing and epidemiology in the UK, Europe, and North America.

The criticisms are substantial, and Deary has engaged with most of them in print.

Causality is not established, and the statistical moves that might establish it are contested. The central question — whether intelligence protects health, or whether the intelligence–health association is produced by confounding — remains open. Deary and Batty themselves report that adjustment for adult occupational status and educational attainment explains roughly a third and a half of the association respectively, and they raise the possibility that intelligence "launches the person into the better environment, but it is the better environment that causes the health benefits." Counter-evidence runs the other way: a large Norwegian register study of over 720,000 men using family fixed effects found that the IQ–mortality gradient persists within families and is not explained by childhood social class. The debate is genuinely unresolved, and reading Deary on either side of it without the other would be misleading.

The field's own boundaries have been challenged from within epidemiology. In a commentary in the International Journal of Epidemiology responding directly to Deary and Johnson, Archana Singh-Manoux argued that the definition of cognitive epidemiology is too narrow: that "cognitive function and intelligence are not interchangeable concepts," that cognitive function is multi-component with domains that decline at different rates, and that because intelligence is not modifiable while education is, the field would be more useful folded into social epidemiology than maintained as a separate discipline. She also noted that most epidemiologists study cognition as an outcome rather than an exposure, making the proposed definition restrictive.

The cohorts carry selection and generalisation limits. The Lothian Birth Cohorts are drawn from a single Scottish region and two single birth years; participants are, by construction, people who survived to age 70 or 79 and were well enough to travel to a research clinic, which introduces survivorship and healthy-volunteer selection that no statistical adjustment fully removes. Comparing a score obtained at age 11 in 1947 with one obtained at age 70 in 2017 also has to contend with substantial secular changes in test performance — the Flynn effect — which the design handles but does not eliminate.

The subject matter is politically charged, and the Edinburgh group has history. Differential psychology in general, and the study of group differences in cognitive test scores in particular, attracts controversy that attaches to the whole sub-discipline. Deary's doctoral supervisor Chris Brand was dismissed from Edinburgh in 1997 for gross misconduct over public statements about race, intelligence, and paedophilia. Deary has not worked on race differences; his funding has come throughout from mainstream UK research councils and medical charities, and his published positions — including his argument against overadjustment for education — are mainstream positions within intelligence research. But the association has made his field's findings harder to discuss in public than their evidential quality warrants, in both directions.

What is not contested is the data. The Lothian Birth Cohorts produced the clearest evidence psychology has that cognitive differences measured in childhood persist, in measurable form, into the eighth decade of life — and that they matter for how that life ends.