The g factor is shared across different cognitive tasks
Vocabulary, calculation, figure reasoning, and memory require different kinds of work. Yet across many people, someone who scores highly on one cognitive task also tends to score highly on others. The component shared across different cognitive tasks is the general intelligence factor, or g factor.
This tendency for cognitive tasks to correlate positively is called the positive manifold. Since Spearman proposed a general factor in his 1904 study, g has become a central concept for explaining overall performance on intelligence tests.
How g is estimated from positive correlations
The g factor is not a score measured directly by one question. It is a latent variable estimated from correlations among multiple tasks covering vocabulary, reasoning, memory, speed, and other abilities.
Factor analysis separates variation shared across many tasks from variation specific to each task. A vocabulary task includes word knowledge and Symbol Search includes visual search speed, while g represents the pattern of variation they share with other cognitive tasks.
The positive manifold appears broadly across tests and cultures. Researchers continue to debate whether one general ability produces it or whether it emerges from interacting abilities and overlapping cognitive processes.
The difference between the g factor, IQ, and FSIQ
| Term | What it represents |
|---|---|
| g factor | A latent general factor estimated from correlations among cognitive tasks |
| IQ | A standard score locating test performance within a same-age norm group |
| FSIQ | Full Scale IQ calculated by combining major subtests in a particular assessment |
FSIQ strongly reflects g because it combines subtests with different content. But FSIQ is an observed score calculated using the structure and conversion rules of a test, whereas g is a latent variable used to explain relationships among scores. What FSIQ means explains how the composite is calculated and interpreted.
A g loading shows how strongly a task is related to g
A g loading describes how strongly a subtest score is related to the g factor. In a simple one-factor model, a loading of .70 gives a squared value of .49, meaning that 49% of the score variance is shared with g.
An analysis of WAIS-IV found comparatively high g loadings for subtests such as Arithmetic and Vocabulary and lower loadings for processing-speed tasks. A g loading is not item difficulty. It can also vary with the population, the set of tests, and the statistical model.
Intelligence tests combine different kinds of task so that the overall score captures a broad common level rather than depending on one kind of knowledge or problem format.
The g factor is strongly related to academic learning and training
Meta-analyses of academic achievement and training and job performance show that the strength of the relationship depends on the outcome.
| Outcome | Correlation after adjusting for measurement limitations |
|---|---|
| Academic achievement | .54 |
| Job training | .35–.49 |
| Contemporary job performance | .18–.22 |
g is a strong predictor of learning in education and training, while its relationship with contemporary job performance is smaller than older summaries often suggested. The contemporary data also did not support the traditional claim that g predicts performance more strongly as job complexity rises. The value of measuring IQ explains how to connect the overall level with real outcomes without treating it as the only influence.
The g factor and CHC broad abilities describe different levels
CHC theory organizes intelligence into general, broad, and narrow abilities. In the commonly used Carroll-style representation, g sits above broad abilities such as Gc, Gf, Gv, Gwm, and Gs. Horn's original model did not place a single g factor at the top.
The g factor represents the level shared across cognitive tasks. Broad abilities show the kinds of task in which a person is more or less likely to perform well. People with similar overall IQ can therefore have different combinations of verbal comprehension, reasoning, visuospatial processing, working memory, and processing speed. Understanding cognitive profiles shows how to connect those combinations to specific situations.
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