The study of intelligence is one of the subjects that attracts most interest, and it is easy to guess why this is so. On the one hand, the capacity to adapt to varied situations is something that is widely considered in an increasingly demanding labour market that always seeks maximum productivity from the worker.

On the other hand, on a much more subjective level, intelligence has become a defining issue of one’s identity and that affects self-image and self-esteem. However, intelligence may seem too abstract and general a concept to be assimilated by science. How is this problem dealt with from psychometry ?

The two factors of intelligence

In the study of intelligence there are different paradigms, such as that of fluid intelligence and crystallised intelligence. However, it is the Bifactorial Theory of the English psychologist Charles Spearman (1863 – 1945) that has perhaps had more notoriety historically.

Spearman observed that the scores that school-age children earned in each of the subjects showed a direct relationship, so that a schoolboy who scores very well in one subject will tend to score well in the other subjects as well. Based on this fact, he devised an explanatory model on intelligence suitable as a starting point for measuring IQ ( CI ). This explanatory model is called Bifactorial Theory of Intelligence .

According to this theory, intelligence, which is the theoretical construct measured by IQ tests, has two factors:

G Factor

A general factor of intelligence , the so-called G Factor , which is the essential foundation of intelligent behaviour in any situation, however particular it may be.


A series of specific factors, which can be understood as skills and aptitudes that are present only in certain areas of life and whose results cannot be generalized to other domains.

A good example to explain the Bifactorial Theory can be found in the case of the video games Brain Training. These video games seem to be designed to improve our G-factor through play. That is, a few hours of play per week should produce the result in the person playing them of a higher intelligence in any situation. However, it seems that they only act on the S Factors: one sees an increase in their ability to play, but this improvement is not generalised to other areas, it is a specific learning process whose results do not go beyond the video game itself .

From the abstract to the concrete

We can agree with Spearman that if anything characterizes intelligence it is its abstract nature . In the study of intelligence there is a paradox in trying to explain something that is defined by changing all the time in its adaptation to the different problems we live with: our capacity to successfully solve the infinitely varied series of problems with scarce resources (among them, time). In this sense, it seems necessary to give an account of something similar to G Factor .

However, by including an abstract concept as the general factor of intelligence, this theoretical model becomes impractical if it is not based on concrete data, on what we find empirically through IQ measurements. For this reason, in addition to coining the term G Factor , Spearman also devised a strategy to empirically arrive at concrete values that would define it. Thus, when is used to operationalize concepts to build tools for measuring intelligence (the IQ test), the G Factor is defined as the representation of the variance common to all the cognitive tasks that are measured by the test. This internal structure of the relationships between the data is found through the use of factor analysis.

Speraman thought that intelligence consisted of knowing how to perform a series of tasks and that the smartest people knew how to do all the tasks well. The different tasks he proposed in the IQ test could be organized into three groups (visual, numerical and verbal), but they were all correlated. This last factor, resulting from the study of these correlations, would be the significant one.

Therefore, the G-Factor that is reflected by the tests is actually a quantifiable measure that can only be found by statistical operations from the raw data collected in each of the test tasks. In contrast to the so-called observable variables , Spearman’s G Factor shows us a matrix of correlations between variables that can only be found by means of the statistical technique. That is, it makes visible the structure of relationships between various variables to create a general value that was hidden, the value of Factor G .

The G Factor, today

Nowadays every intelligence test can be based on different theoretical frameworks and conceptions of intelligence , precisely because of the abstract nature of this last concept. However, it is common for these measurement tools to include scores on specific areas of competence (language, spatial intelligence, etc.) at various levels of abstraction, and also to offer a G Factor as a value which summarises the general intelligence of the individual. It can be considered that many forms of intelligence measurement are direct descendants of Spearman’s theory.

IQ tests are intended to measure intelligence psychometrically as a function of genetic or “g” variables. This is an indicator which is usually used in academic environments or to detect possible developmental disorders (such as maturity delays) and which is also used to establish correlation relations between the environment and the genetic components of intelligence: the G Factor has been correlated with life expectancy, the possibility of finding work and other relevant constructs .

Criticism and discussion

There are basically two criticisms that can be made of him. The first is that the general intelligence factor seems to be affected by the cultural bias : the economic position, educational level and geographical distribution of housing seems to affect intelligence results, and this is a question that cannot be explained only by genetic variation. The second is that, however practical it may be, the G Factor is insensitive to the different forms of manifestation of intelligence , the particularities that make each person develop intelligent behaviour in his or her own way (something that has been tried to be corrected from the model of multiple intelligences of Howard Gardner, for example).

In any case, it is clear that the G Factor is a very interesting concept for research in psychology and social sciences.