The secular trend of intelligence test scores: The Danish experience for young men born between 1940 and 2000

The present study investigated the Danish secular trend of intelligence test scores among young men born between 1940 and 2000, as well as the possible associations of birth cohort changes in family size, nutrition, education, and intelligence test score variability with the increasing secular trend. The study population included all men born from 1940 to 2000 who appeared before a draft board before 2020 (N = 1,556,770). At the mandatory draft board examination, the approximately 19-year-old men underwent a medical examination and an intelligence test. In the statistical analyses, the IQ mean and standard deviation (SD) were estimated separately for each of the included annual birth cohorts based on information from birth cohorts with available total intelligence test scores for all tested individuals (i.e. 1940–1958 and 1987–2000; the mean and SD were interpolated for the intermediate birth cohorts). Moreover, the possible associations with birth cohort changes in family size, height as a proxy for nutritional status, education, and IQ variability were investigated among those birth cohorts for whom a secular increase in intelligence test scores was found. The results showed that the estimated mean IQ score increased from a baseline set to 100 (SD: 15) among individuals born in 1940 to 108.9 (SD: 12.2) among individuals born in 1980, since when it has decreased. Focusing on the birth cohorts of 1940–1980, for whom a secular increase in intelligence test scores was found, birth cohort changes in family size, height, and education explained large proportions of the birth cohort variance in mean intelligence test scores, suggesting that these factors may be important contributors to the observed Flynn effect in Denmark.

How Is Intelligence Test Performance Associated with Creative Achievement? A Meta-Analysis

This paper presents a meta-analysis of the links between intelligence test scores and creative achievement. A three-level meta-analysis of 117 correlation coefficients from 30 studies found a correlation of r = .16 (95% CI: .12, .19), closely mirroring previous meta-analytic findings. The estimated effects were stronger for overall creative achievement and achievement in scientific domains than for correlations between intelligence scores and creative achievement in the arts and everyday creativity. No signs of publication bias were found. We discuss theoretical implications and provide recommendations for future studies.

How is Intelligence Test Performance Associated with Creative Achievement? A Meta-Analysis

This paper presents a meta-analysis of the links between intelligence test scores and creative achievement. A three-level meta-analysis of 117 correlation coefficients from 30 studies has found a correlation of r = .16 (95% CI: .12, .19), closely mirroring previous meta-analytic findings. The estimated effects were stronger for overall creative achievement and achievement in scientific domains than for correlations between intelligence scores and creative achievement in the arts and everyday creativity. No signs of publication bias were found. We discuss theoretical implications and provide recommendations for future studies.

Intelligence, alcohol consumption, and adverse consequences. A study of young Norwegian men

Aims: Research suggests that intelligence is positively related to alcohol consumption. However, some studies of people born around 1950, particularly from Sweden, have reported that higher intelligence is associated with lower consumption and fewer alcohol-related problems. We investigated the relationships between intelligence, alcohol consumption, and adverse consequences of drinking in young men from Norway (a neighboring Scandinavian country) born in the late 1970s. Methods: This analysis was based on the population-based Young in Norway Longitudinal Study. Our sample included young men who had been followed from their mid-teens until their late 20s ( n = 1126). Measures included self-reported alcohol consumption/intoxication, alcohol use disorders (AUDIT), and a scale measuring adverse consequences of drinking. Controls included family background, parental bonding, and parents’ and peers’ drinking. Intelligence test scores—scaled in 9 “stanines” (population mean of 5 and standard deviation of 2)—were taken from conscription assessment. Results: Men with higher intelligence scores reported average drinking frequency and slightly fewer adverse consequences in their early 20s. In their late 20s, they reported more frequent drinking than men with lower intelligence scores (0.30 more occasions per week, per stanine, age adjusted; 95% CI: 0.12 to 0. 49). Intelligence was not associated with intoxication frequency at any age and did not moderate the relationships between drinking frequency and adverse consequences. Conclusions: Our results suggest that the relationship between intelligence and drinking frequency is age dependent. Discrepancies with earlier findings from Sweden may be driven by changes in drinking patterns.

6. What do more intelligent brains look like?

‘What do more intelligent brains look like?’ considers a study that used data from the Lothian Birth Cohort 1936 to test the strength of the correlation between the general intelligence scores of the participants and different measures of their brain’s structure. Magnetic resonance imaging was used to measure total brain volume, brain cortical thickness, brain white matter integrity (or health), and brain white matter hyperintensities. The study showed that people who have higher general intelligence tend to have larger brains, thicker grey matter on the surface of the brain, and healthier white matter brain connections. The associations are not strong, but some aspects of brain structure do relate to intelligence test scores.

8. Does intelligence matter for health and longer life?

The new field of cognitive epidemiology looks at whether intelligence tests might have some predictive power in health, and even for death. ‘Does intelligence matter for good health and long life?’ discusses the results of various studies that link the results of intelligence tests at age 11 with medical records in later life. The results show that there is a robust association between higher intelligence test scores in early life and living longer, and having a lower risk of dying from several causes. They also show that, on average, people with higher childhood intelligence have a lower risk of developing various illnesses and are more likely to adopt healthier behaviours as adults.

7. Does intelligence matter in the school and the workplace?

Do intelligence test scores have some predictive power? Can they predict who will do well in achieving more and better educational qualifications, and after school, can they predict who will perform well in the workplace? ‘Does intelligence matter in the school and the workplace?’ looks at the use of the Cognitive Abilities Test in United Kingdom schools and its correlation with GCSE results five years later. The correlation is high: people’s intelligence differences at age 11 are a powerful predictor of their differences in educational outcomes at age 16. In the workplace, the use of general intelligence/psychometric testing in selecting people for work is worthwhile. Intelligence predicts occupational and educational successes.

Body height in young adult men and risk of dementia later in adult life

This study examined the relationship between body height and dementia and explored the impact of intelligence level, educational attainment, early life environment and familial factors. A total of 666,333 men, 70,608 brothers, and 7388 twin brothers born 1939–1959 and examined at the conscript board were followed in Danish nationwide registers (1969–2016). Cox regression models were applied to analyze the association between body height and dementia. Within-brothers and within-twin pair analyses were conducted to explore the role of shared familial factors including partly shared genetics. In total, 10,599 men were diagnosed with dementia. The association between one z-score difference in body height and dementia (HR: 0.90, 95% CI: 0.89;0.90) was inverse and weakened slightly after adjustment for intelligence test scores and educational level. The associations persisted in within-brother analysis and revealed a stronger, but less precise, point estimate than the cohort analysis of brothers. The twin analysis showed similar, but imprecise estimates.