Letter to the Editor |
RE: "CHILDHOOD COGNITIVE PERFORMANCE AND RISK OF MORTALITY: A PROSPECTIVE COHORT STUDY OF GIFTED INDIVIDUALS"
Department of Basic Psychological Research, School of Psychology, University of Vienna, A-1010 Vienna, Austria
(e-mail: martin.voracek{at}univie.ac.at)
In a recent Journal article, Martin and Kubzansky (1
) used data from the classic Terman Genetic Study of Genius (2, 3), the longest follow-up study in the social sciences, to test whether childhood psychometric intelligence is positively related to longevity (4). Their findings from the Terman cohort favored this hypothesis. Suicide mortality may be an exception to the observed association between high cognitive performance and longevity. This neglected and widely unrecognized outcome from Terman's study should stimulate further research in this area.
For the unique study initiated by Terman (now called the Terman Life Cycle Study of Children with High Ability), 1,528 gifted children (857 boys and 671 girls), mostly 11-year-olds, were identified in California public schools in 1921–1922 and were followed throughout their entire life cycle (3). Owing to the inclusion criterion of a Stanford-Binet intelligence quotient of 140 or higher, all study participants ranked within the 99th percentile of the population distribution of psychometric intelligence, and the cohort's mean intelligence quotient was 151.
Various investigators have studied the suicides that occurred among these highly intelligent individuals (2, 5–9). Surprisingly, these accounts altogether lack any appreciation of the obviously increased suicide mortality in this group. As of 1960, 14 male and eight female suicides had been recorded within the Terman cohort (2); as of 1970, 20 male and eight female suicides had been recorded (5); and as of 1987 (at a median participant age of 75 years or more), 25 male and nine female suicides were known—meaning that up to this endpoint, one out of every 11 male deaths and one out of every 19 female deaths in this cohort was due to suicide (8). There appears to have been no update of the numbers of suicides since then. Therefore, a conservative (minimum) estimate of the Terman cohort's lifetime suicide mortality rate is 2.2 percent. This is notably high, since the corresponding figure for noninstitutionalized populations not suffering from affective disorders is less than 0.5 percent (10). Alternatively, simply imputing the maximal number of observable person-years (100,848) over the 66-year follow-up period of 1921–1922 to 1987 (i.e., 1,528 subjects x 66 years), which likewise is a conservative assumption, yields a mean suicide density rate of 33.7 per 100,000 person-years. This is also a high suicide mortality figure for a US context, since the median of annual US suicide rates from 1950 to 1985 was 11.1 per 100,000 inhabitants per year (11).
It is entirely conceivable that at higher intelligence levels there is increased mortality from one infrequent cause of death (suicide) which is, so to speak, "hidden"—that is, more than offset by the same group's reduced mortality from all other causes combined—because the latter causes constitute a much larger portion than suicide. This appears to be the case for the Terman cohort. More generally, risk of suicide could be an exception to the observed link between high intelligence and reduced mortality. Elsewhere (12–16), I reviewed various lines of evidence from suicide research and presented novel data from geographic studies which are supportive of this conjecture. To explore this topic further, it would be beneficial to scrutinize the life course and fate of the ascertained suicide victims within the Terman study, as well as within other longitudinal studies with appropriate databases, such as the Scottish Mental Health Survey of 1932 (4).
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Martin LT, Kubzansky LD. Childhood cognitive performance and risk of mortality: a prospective cohort study of gifted individuals. Am J Epidemiol 2005;162:887–90.
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- Shneidman ES. Perturbation and lethality as precursors of suicide in a gifted group. Life-Threat Behav 1971;1:23–45.
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[Abstract/Free Full Text] - Lester D, Yang B. Suicide and homicide in the twentieth century: changes over time. Commack, NY: Nova Science Publishers, 1998.
- Voracek M. Risk of suicide in twins: intelligence of twins and singletons may explain risk. (Letter). BMJ 2003;327:1168.
[Free Full Text] - Voracek M. National intelligence and suicide rate: an ecological study of 85 countries. Pers Individ Dif 2004;37:543–53.
- Voracek M. National intelligence, suicide rate in the elderly, and a threshold intelligence for suicidality: an ecological study of 48 Eurasian countries. J Biosoc Sci 2005;37:721–40.[Medline]
- Voracek M. The social ecology of intelligence and suicide in Belarus. J Soc Psychol 2005;145:613–17.[Medline]
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  L. T. Martin and L. D. Kubzansky THE AUTHORS REPLY Am. J. Epidemiol., June 15, 2006; 163(12): 1162 - 1163. [Full Text] [PDF]
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