Some epidemiological research on the subject has shown that there is a small but statistically significant positive correlation between height and intelligence after controlling for socioeconomic class and parental education.
[1] The cited study, however, does not draw any conclusions about height and intelligence, but rather suggests "a continuing effect of post-natal growth on childhood cognition beyond the age of 9 years."
[2] One such theory argues that since height strongly correlates with white and gray matter volume, it may act as a biomarker for cerebral development which itself mediates intelligence.
[8] The motive for this research was to attempt to predict the potential “dullness” or “precocity” of children based on simple measurements teachers could make.
In 2014, another study was carried out by a team of researchers at Edinburgh University, Scotland, motivated by the understanding that both height and intelligence test scores are predictors of better health outcomes and mortality.
The study was constructed to better identify if there are any shared phenotypic and genetic influences from height and intelligence in determining health outcomes and mortality.
In most of the studies, intelligence quotient (IQ) tests were used to measure a subject's mental age, which was checked for possible correlation with height.
[12][13] While the use of IQ tests are highly debated among scientists as an accurate measurement of intelligence, they provide a quantitative and normal distribution to compare cognitive abilities among people.
[15] Regardless, studies conducted to compare height with intelligence frequently use the Wechsler Adult Intelligence Scale (WAIS) which measures verbal and performance abilities for individuals over the age of 16 (WISC for those under 16) years through the following tests: information, general comprehension, memory span, arithmetical reasoning, similarities, vocabulary, picture arrangement, picture completion, block design, object assembly, and a digit symbol test.
[16] Many of the studies performed on the relationship between physical stature and intelligence used one of these tests in order to gauge relative cognitive ability based on the age of the participants.
Both the Wechsler Intelligence Scale for Children and the Wide Range Achievement Test were found to significantly correlate with height.
127 growth-restricted and 32 non-growth-restricted children aged 9 to 24 months were put on a two-year "randomized trial of nutritional supplementation and psychosocial stimulation."
This study found that among children of school age, there is a correlation of about 0.15-0.25 between height and score on the 11+ test, an examination administered to students in England.
[25] There was weak or no correlation between cognitive ability and height found when examining ten brain measurements from a large elderly population, even when controlled for sex and age.
[26] There is an increase in brain development during the adolescent years and a marked decrease afterwards, despite height generally staying constant after reaching adulthood.
Common percent values range between 60 and 80%,[28] with high variation attributed to differences in a population's genetic history and environment (such as climate, nutrition, and lifestyle).
The most notable contributing environmental influences associated with the correlation of height and IQ include “diet, disease, psychosocial stress and inadequate cognitive stimulation”[29] Populations that live under stable conditions tend to have higher values of genetic influence, while populations susceptible to events of poor nutrition and illness show greater determination from their environment.
[37] It's also important to note that several of the recent studies confirming the correlation employed the standard bivariate ACE model,[22][36][37] which is extremely sensitive to assumptions reflected in parameters.
For instance, two of these studies arrived at similar estimates for the relative responsibility of common environmental and genetic factors in causing the correlation: 59% and 59% for the former, 31% and 35% for the latter.
[22][36] However, only slight modifications to the coefficient of assortative mating made the difference between the inferred percentage of genetic responsibility being as low as around 30% (the value the authors reported) to as high as 90%.
[22] Further, another study using the same model even concluded that genetics alone could explain the correlation, without any influence from common environmental factors such as one's education level and nutrition.