Social ecology of intelligence and suicide in the United States

The big g‐factor of national cognitive ability

The response deals with several controversial issues: theoretical concepts of cognitive abilities, their cultural relativity in definition or level, the meaning and validity of national cognitive ability, methodological questions like the ecological fallacy, the variance of intelligence at different levels of observation, multi‐level analysis, the correctness and importance of levels of analysis in cognitive‐ability research, the aggregation and adjustment process, and the similarities of different cognitive assessment approaches. Central to this research are questions of causality (the causes and consequences of national cognitive‐ability homogeneity and level), of malleability of these levels, and of ethical and political consequences of intelligence research. Copyright © 2007 John Wiley & Sons, Ltd.

Regional Intelligence and Suicide Rate: New Data for Australia and a Synthesis of Research

Previous research has shown for the most part positive correlations between intelligence and suicide prevalence on the national level. However, this study found proxies for regional intelligence in Australia (international average domain scores from the PISA 2000 study) to be significantly negatively correlated with the total, male, and female suicide rates of the different administrative divisions of Australia, and this finding was independent of regional wealth. A research synthesis of the current results and those from similar studies of other countries (positive correlations for Austria, Belarus, The British Isles, Denmark, and The Netherlands; inconclusive findings for France, Germany, and the USA) was conducted. This synthesis of research findings showed that positive ecological correlations of intelligence with suicide rate were more likely observed for nations with higher suicide rates and poorer general living conditions, whereas there was no relation with national IQ.

State IQ and Suicide Rates in the United States

Previous findings pertaining to the direction (positive or negative) of the ecological correlation between intelligence and suicide rates in the USA have been conflicting. Using novel state IQ estimates, derived from the Scholastic Assessment Test, the American College Test, these tests combined, or the National Assessment of Educational Progress state scores, these estimates were not consistently associated to state suicide rates. Whereas ACT-derived state IQ was significantly positively correlated with suicide rates, the correlation with composite ACT-SAT-derived state IQ was significantly negative and with both SAT-derived and NAEP-derived state IQ also negative but not significant. Validity checks pointed to possible methodological problems with the state IQ estimates. Currently available estimates of state IQ, therefore, seem not appropriate to resolve the question of the direction of the ecological correlation of intelligence and suicide mortality across the USA.

Evidence for a Positive Ecological Correlation of Regional Intelligence and Suicide Mortality in the United States during the Early 20th Century

Several contemporary cross-national and intranational geographic studies have reported positive ecological (group-level) associations of intelligence and suicide mortality. These findings are consistent with facts from suicide research and with an evolutionary view of suicidal behavior. The present research extended these accounts cross-temporally. Analysis of E. L. Thorndike's state-level personal quality scores and standardized birth rates of eminent persons, taken as proxy variables for regional intelligence, along with historical state suicide rates (1913–1924 and 1928–1932) showed that intelligence and suicide mortality across the USA were already clearly positively related during the early 20th century, suggesting time stability of the effect. Within the USA, the effect is possibly due to state differences in the ethnic composition, which correspond to both suicide rates and intelligence proxies. It is argued that the most parsimonious interpretation of these ecological findings remains that they indeed reflect individual-level effects, that a positive link between intelligence and suicide is entirely compatible with positive overall links between intelligence and health and longevity, and that the ultimate explanative background for the positive link between intelligence and suicide may be provided through the framework of Rushton's differential K theory.

Regional Intelligence and Suicide Rate in Germany

Regional intelligence proxies (intranational average domain scores from the PISA 2000 and 2003 studies) were not reliably associated with the suicide rate across the states of Germany, thereby not replicating findings of a positive ecological correlation of regional intelligence and suicide prevalence from other within-nation studies (Austria, Belarus, the British Isles, Denmark, The Netherlands, and the USA).

National Differences in Intelligence and Population Rates of Suicidal Ideation, Suicide Plans, and Attempted Suicide

Population rates of suicidal ideation, suicide plans or attempted suicide from three independent multinational epidemiological surveys (the WHO/EURO and WHO SUPRE-MISS studies and a third one) were not significantly associated with national IQ figures. This result conflicts with previous evidence from cross-national studies (by Lester and by Voracek) of a positive ecological correlation between level of national intelligence and rates of completed suicide. Across nations, the indicators for the prevalence of suicidal behavior also lacked close correspondence with suicide rates, which may be due to the higher unreliability of assessing covert suicidal behavior (suicide ideas, thoughts, plans, and, to a lesser extent, also suicide attempts) as compared to suicidal behavior that is indisputably overt (completed suicide). Several alternative explanations for the current nil findings are also discussed.

National Intelligence and Suicide Rate across Europe: An Alternative Test Using Educational Attainment Data

National mean scores on a historical knowledge test (taken as a proxy for intelligence), stemming from representative samples of male (and female) 9th-grade school students from 26 European countries in a 1999 report by Wilberg and Lynn, were significantly positively associated with the national male (and female) suicide rates, independent of the general quality-of-living conditions in these countries. This finding replicates previous evidence from cross-national studies (by Lester and by Voracek), of a correspondence of higher national IQ to higher suicide rates, with an alternative measure of national IQ that is independent of the national IQ estimates recently published by Lynn and Vanhanen which have been used in prior studies.

The Nexus of Suicide Prevalence, Helping Behavior, Pace of Life, Affluence, and Intelligence: Contrary Results from Comparisons across Nations and within the United States

This study examined interrelations among suicide prevalence, affluence, intelligence, pace of life, and helping behavior on the level of aggregate analysis, both cross-nationally and within the USA, using four extant data sets (8, 15, and 29 countries; and 17 U.S. states) for the latter two variables. Pertaining to the association of suicide rates with pace of life, the results replicated discrepant previous findings of Lester. Across nations, suicide is more prevalent in populations living in faster environments, whereas within the USA suicide rates are higher in slower environments. Further, seen from an international perspective, there appears to be a nexus of variables, such that more people tend to commit suicide in the more affluent and faster environments which are populated by more intelligent, but less friendly, individuals. Within the USA, the direction of the correlations of suicide prevalence with these four variables is exactly reversed. Possible reasons for these opposed findings and implications for research are discussed.

Elderly suicide rates: the importance of a non-linear relationship with distal risk and protective factors

The elderly population size is increasing worldwide due to prolonged life expectancy and falling birth rates. Traditionally, suicide rates increase with age. For example, a recent cross-national study of 62 developing and developed countries reported an increase in suicide rates with aging in males and females in 25 and 27 countries respectively (Shah, 2007a). Thus, suicides in the elderly are an important public health concern. While much is known about proximal (individual level) risk and protective factors for elderly suicides (e.g. Conwell et al., 1991; Cattell and Jolley, 1995; Harwood et al., 2001), less is known about more distal (societal or population level) risk and protective factors (Rehkopf and Buka, 2006). Moreover, detailed knowledge of these distal factors may have greater public health relevance for the development of comprehensive prevention strategies (Knox et al., 2004).

Regional Intelligence and Suicide Rate in Italy

Replicating the majority finding from prior related studies of European countries, regional IQ estimates and suicide rates in Italy were positively correlated; the association was retained with application of controls for regional affluence. Directions for further inquiry into aggregate-level associations of cognitive-ability indicators and suicide risk within nations are discussed.

Big five personality factors and suicide rates in the United States: a state-level analysis

Partly replicating findings from several cross-national studies (of Lester and of Voracek) on possible aggregate-level associations between personality and suicide prevalence, state-level analysis within the United States yielded significantly negative associations between the Big Five factor of Neuroticism and suicide rates. This effect was observed for historical as well as contemporary suicide rates of the total or the elderly population and was preserved with controls for the four other Big Five factors and measures of state wealth. Also conforming to cross-national findings, the Big Five factors of Agreeableness and Extraversion were negatively, albeit not reliably, associated with suicide rates.

The relationship between general population suicide rates and educational attainment: a cross-national study

Suicides are associated with both high and low levels of intelligence and educational attainment in both individual-level and aggregate-level studies. A cross-national study examining the relationship between general population suicide rates (y) and educational attainment (x) was undertaken with the a priori hypothesis that the relationship would be curvilinear and follow a U-shaped curve with the quadratic equation Y = A + BX + CX(2), where A, B, and C are constants. Data on suicide rates and the Education Index (a proxy measure of educational attainment) were ascertained from the World Health Organization and the United Nations Web sites, respectively. The main finding was the predicted curvilinear relationship between general population suicide rates, in both sexes, and the Education Index fit the above quadratic equation. Given the cross-sectional study design, a causal relationship cannot be assumed. The impact of educational attainment on general population suicide rates may occur through interaction with other factors, mediation of the effects of other factors, or by its effects being mediated by other factors, and require further study.

Is there a relationship between elderly suicide rates and educational attainment? A cross-national study

BACKGROUND

Suicides are associated with both high and low levels of intelligence and educational attainment in both individual-level and aggregate-level studies, but this has been rarely studied in the elderly.

METHODS

A cross-national study examining the relationship between elderly suicide rates (y-axis) and educational attainment (x-axis) was undertaken with the 'a priori' hypothesis that the relationship would be curvilinear and follow a U-shaped curve with the quadratic equation Y = A + BX + CX(2), where A, B and C are constants. Data on suicide rates for both sexes in the age-bands 65-74 years and 75+ years, and the Education Index (a proxy measure of educational attainment) were ascertained from the World Health Organisation and the United Nations websites, respectively.

RESULTS

The main finding was the predicted curvilinear relationship between suicide rates, in both sexes in both the elderly age-bands, and the Education Index fitting the quadratic equation Y = A + BX + CX(2).

CONCLUSIONS

Given the cross-sectional study design, a causal relationship cannot be assumed. The impact of educational attainment on elderly suicide rates may occur through interaction with other factors, mediation of the effects of other factors, or by its effects being mediated by other factors, and require further study.

Cross-National Social Ecology of Intelligence and Suicide Prevalence: Integration, Refinement, and Update of Studies

This study integrates, refines, and updates previous findings pertaining to positive ecologic (population-level) associations between intelligence and suicide prevalence across nations by using corrected and revised national IQ estimates and, further, a quality-of-human-conditions index, both recently published by Lynn and Vanhanen. Across a global 85-nation sample of sex-specific total suicide rates and a Eurasian 48-nation sample of sex-specific elderly suicide rates, these were positively associated with updated national IQ estimates. The associations were stronger for the general population than for elderly persons, independent of the quality of human conditions, and notedly stronger in exponential fitting of suicide rates with national IQ than in linear fitting, thereby indicating that shifts or differences in national IQ correspond to proportional, not absolute, changes in suicide rates. Implications of these findings and the question of generalizability of such associations to the individual level are discussed.

State IQ and Elderly Suicide Rates in the United States

Paralleling previous findings with state suicide rates of the total population, the associations of state suicide rates of elderly persons with regional IQ estimates across the USA were inconsistent (positive, negative, or nil), depending on the source of available state IQ estimates used in the analysis. The implications of these findings and directions for further inquiry are discussed.

Surname study of suicide in Austria: differences in regional suicide rates correspond to the genetic structure of the population

OBJECTIVES

There is convergent evidence from adoption, family, geographical, immigrant, molecular genetic, twin and, most recently, surname studies of suicide for genetic contributions to suicide risk. Surnames carry information about genetic relatedness or distance and, in patrilineal surname systems, are a close substitute for Y-chromosome markers and haplotypes, since surname transmission is similar to the transmission of the nonrecombining part of the Y chromosome. This study investigated whether differences in regional suicide rates correspond to the genetic structure of the Austrian population.

METHODS

Differences in district-level standardized suicide rates 1988-94 between the five major surname regions identified for Austria were analyzed. The surname regions used in the analysis reflect the contemporary population structure and closely follow the natural borders found in the topography of Austria, less so its administrative division into nine states.

RESULTS

Surname region accounted for a significant (P < 0.001) and substantial (38%) portion of the variance in district-level suicide rates. Adjusting the suicide rates for a set of five social and economic indicators that are established ecological correlates of suicide prevalence (income, and rates of the divorced, unemployed, elderly and Roman Catholics) left the results essentially unchanged.

CONCLUSIONS

Regional differences in suicide rates within Austria correspond to the genetic structure of the population. The present evidence adds to related findings from geographical and surname studies of suicide that suggest a role for genetic risk factors for suicidal behavior. Genetic differences between subpopulations may partially account for the geography of suicide. Study limitations and directions for future research are discussed.