Chapter 6 – The Real Error of Cyril Burt

Factor Analysis and the Reification of Intelligence

The Case of Sir Cyril Burt

Throughout his career, British educational psychologist, Sir Cyril Burt, led the intelligence testing charge for London schools and later became psychology department chair at the University of London. After retiring, he published several papers on intelligence in identical twins, claiming to have found twin IQ scores were very similar, even if the twins were raised in different environments. Burt’s papers added a great deal of support to the hereditarian position that intelligence is inherited, not shaped by outside factors.

However, Burt’s claims did not add up. Other psychologists took a look at his data and determined he had, in fact, made most of the numbers up. In addition, Burt falsely claimed to be  the inventor of a statistical technique called factor analysis, stealing credit from Charles Spearman. 

Given his Burt’s wrongful actions, Gould attempts to set the record straight, as understanding factor analysis is key to the proper interpretation of intelligence testing results.


Correlation, Cause, and Factor Analysis

Gould first explains the difference between correlation and causation. Correlation assesses the tendency of one factor to vary in conjunction with another. But just because two factors are correlated does not mean one of them is causing the other. Correlation and causation comparisons are made when only two factors exist, but it gets more complex when three or more factors are being compared. This is where factor analysis comes into play.

Factor analysis is a complicated mathematical technique that uses matrices, vectors, coefficients, sines, and cosines to simplify dozens of correlations into just a handful of comparison in order to more clearly understand them. Thus, factor analysis is useful for better understanding a large collection of data. However, Gould urges readers to remember the math behind factor analysis is still just a series of numbers; it does not describe anything physical that exists in the world; it simply helps scientists talk about measurements. Remember reification?


Charles Spearman and General Intelligence

In 1904, Charles Spearman did just this; he reified the data from his factor analysis of mental intelligence tests and labeled it g for general intelligence. Spearman believed g pointed to a single mental capability called intelligence that lay at the center of all cognitive skills. Though he also believed general intelligence was inheritable and unalterable, he claimed specific abilities could be improved through training and education. 


Cyril Burt and the Hereditarian Synthesis

Spearman used factor analysis simply to better understand intelligence and the brain; it was never his intent to apply the results of his intelligence tests to the real world. Sir Cyril Burt was the one who took it one step further. 

Burt’s belief that students’ innate intelligence could be measured and ranked by IQ tests had lasting effects for generations of British students. Students began being tested at the age of 10 or 11, and their scores determined what kind of secondary school they could attend. Secondary school students were also tested, and only a portion were deemed suitable for college preparatory schools; the rest were sent to technical schools and banned from attending universities. 


L.L. Thurstone and the Vectors of Mind

Psychology professor at the University of Chicago, L.L. Thurstone, is best known for debunking Spearman’s g, as he believed g failed to represent something real and factor analysis failed to correctly characterize general intelligence. In doing so, Thurstone invented a new vector method. 

Gould once again points out the error of Thurstone’s ways: his correction to the factor analysis method was not based on any new evidence or test data, it was simply a decision he made based on a pre-existing belief that IQ tests do indeed measure some real mental ability. 


A Final Thought

As a final thought, author Stephen Jay Gould includes a single quote from 19th century English philosopher John Stuart Mill, urging readers to remember the concept of reification: “The tendency has always been strong to believe that whatever received a name must be an entity or being, having an independent existence of its own.”