Psychometrics Quotes

“If one chooses to call tests that require the mastery of abstractions culturally biased, because some cultures put more emphasis on abstractions than others, that raises fundamental questions about what the tests are for. In a world where the ability to master abstractions is fundamental to mathematics, science and other endeavors, the measurement of that ability is not an arbitrary bias. A culture-free test might be appropriate in a culture-free society—but there are no such societies.”
― Thomas Sowell, Intellectuals and Society

“The smartest person to ever walk this Earth in all probability lived and died herding goats on a mountain somewhere, with no way to disseminate their work globally even if they had realised they were super smart and had the means to do something with their abilities.

I am not keen on 'who are the smartest' lists and websites because, as Scott Barry Kaufman points out, the concept of genius privileges the few who had the opportunity to see through and promote their life’s work, while excluding others who may have had equal or greater raw potential but lacked the practical and financial support, and the communication platform that famous names clearly had.

This is why I am keen to develop, through my research work, a definition of genius from a cognitive neuroscience and psychometric point of view, so that whatever we decide that is and how it should be measured, only focuses on clearly measurable factors within the individual’s mind, regardless of their external achievements, eminence, popularity, wealth, public platform etc. In my view this would be both more equitable and more scientific.”
― Gwyneth Wesley Rolph

“When studies using mental ability test scores from children are considered, the heritability of mental ability is typically found to be about .40, and the effect of the common or shared environment is found to be almost as strong, about .35. In contrast, when studies using mental ability test scores from adults (or older adolescents) are considered, estimates of the heritability of mental ability are much higher, typically about .65, whereas estimates of common or shared environment effects are much lower, probably under .20 (see review by Haworth et al., 2010). These findings indicate that differences among children in their levels of mental ability are attributable almost as much to their common environment—that is, to features of their family or household circumstances—as to their genetic inheritances. However, the findings also suggest that as children grow up, the differences among them in mental ability become less strongly related to the features of their common environments, and more strongly related to their genetic inheritances. In other words, the effect on one's mental ability of the family or household in which one is reared tends to become less important as one grows up, so that by adulthood one's level of mental ability is heavily dependent on one's genetic characteristics. It is as if one's level of mental ability—relative to that of other persons of the same age—can be raised (or lowered) during childhood by a particularly good (or poor) home environment, but then gradually returns to the level that one's genes tend to produce.”
― Michael C. Ashton, Individual Differences and Personality

“When studies using mental ability test scores from children are considered, the heritability of mental ability is typically found to be about .40, and the effect of the common or shared environment is found to be almost as strong, about .35. In contrast, when studies using mental ability test scores from adults (or older adolescents) are considered, estimates of the heritability of mental ability are much higher, typically about .65, whereas estimates of common or shared environment effects are much lower, probably under .20 (see review by Haworth et al., 2010). These findings indicate that differences among children in their levels of mental ability are attributable almost as much to their common environment—that is, to features of their family or household circumstances—as to their genetic inheritances. However, the findings also suggest that as children grow up, the differences among them in mental ability become less strongly related to the features of their common environments, and more strongly related to their genetic inheritances. In other words, the effect on one's mental ability of the family or household in which one is reared tends to become less important as one grows up, so that by adulthood one's level of mental ability is heavily dependent on one's genetic characteristics. It is as if one's level of mental ability—relative to that of other persons of the same age—can be raised (or lowered) during childhood by a particularly good (or poor) home environment, but then gradually returns to the level that one's genes tend to produce.

The aforementioned findings are based mainly on samples of participants who belong to the broad middle class of modern Western countries. There is some evidence, though, that the heritability of IQ tends to be somewhat lower (at least until young adulthood, and perhaps beyond) when studies are conducted using participants of less enriched environments, such as those in economically underdeveloped countries or in the lowest socioeconomic classes of some Western countries (see review by Nisbett et al., 2012). One recent study (Tucker-Drob & Bates, 2016) found that in the United States, additive genetic influences had a weaker influence on IQ among persons of low socioeconomic status than among persons of high socioeconomic status. (Interestingly, Tucker-Drob and Bates did not find this effect in western European countries or in Australia, where socioeconomic status differences tend to be smaller.) The above findings suggest that whenever the heritability of IQ is discussed, it is important to consider the ages of the persons being examined as well as their socioeconomic status and their country.”
― Michael C. Ashton, Individual Differences and Personality

“Here are ten facts about IQ. These facts are debated and often controversial among the general public but far less so among scientists who
study intelligence. The best review of the academic literature
supporting these facts is a 2012 paper by Richard Nisbett and
colleagues – an interdisciplinary team of leading scholars, household
names within intelligence research, comprised of psychologists, an
economist, a behavioral geneticist, and a former President of the
American Psychological Association. Their areas of expertise include
cultural and sex differences in intelligence, the effect of social and
genetic factors that affect intelligence, the development of intelligence
over the lifespan, the relationship between economic development
and intelligence, and changes in intelligence over history

1. IQ is a good predictor of school and work performance, at least in WEIRD societies.

2. IQ differs in predictive power and is the least predictive of performance on tasks that demand low cognitive skill.

3. IQ may be separable into what can be called ‘crystallized intelligence’ and ‘fluid intelligence’. Crystalized intelligence refers to knowledge that is drawn on to solve problems. Fluid intelligence refers to an ability to solve novel problems and to learn.

4. Educational interventions can improve aspects of IQ, including fluid intelligence, which is affected by interventions such as memory training. Many of these results don’t seem to last long, although there is strong evidence that education as a whole causally raises IQ over a lifetime.

5. IQ test scores have been dramatically increasing over time. This is called the Flynn effect after James Flynn (also an author of the review mentioned above), who first noticed this pattern. The Flynn effect is largest for nations that have recently modernized. Large gains have been measured on the Raven’s test, a test that has been argued to be the most ‘culture-free’ and a good measure of fluid intelligence. That is, it’s not just driven by people learning more words or getting better at adding and subtracting.

6. IQ differences have neural correlates – i.e. you can measure these differences in the brain.

7. IQ is heritable, though the exact heritability differs by population, typically ranging from around 30% to 80%.

8. Heritability is lower for poorer people in the US, but not in Australia and Europe where it is roughly the same across levels of wealth.

9. Males and females differ in IQ performance in terms of variance and in the means of different subscales.

10. Populations and ethnicities differ on IQ performance.

You can imagine why some people might question these statements. But setting aside political considerations, how do we scientifically make sense of this?

Popular books from Richard Herrnstein and Charles Murray’s The Bell Curve (1994) to Robert Plomin’s Blueprint (2018) have attributed much of this to genes. People and perhaps groups differ in genes, making some brighter than others. But humans are a species with two lines of inheritance. They have not just genetic hardware but also cultural software. And it is primarily by culture rather than genes that we became the most dominant species on earth. For a species so dependent on accumulated knowledge, not only is the idea of a culture-free intelligence test meaningless, so too is the idea of culture free intelligence.”
― Michael Muthukrishna