g Theory of Intelligence

The g Factor

The g factor is the most important variable in a g theory of intelligence. In psychology, the g factor is used to explain one of the most remarkable facts—scores on all mental ability tasks correlate positively. These mental ability tasks can include deciphering the logical progression of a complex pattern, recalling numbers backward, and defining words.

Despite the diversity in the universe of mental ability tasks, someone who performs well on one task, on average, also performs well on the other tasks. For example, individuals who perform very well on a task that requires them to manipulate shapes to make a pattern, also on average, perform well on a task that requires them to verbally define words. Although the tasks vary considerably, the performance across the tasks is related. The reason the performance is related is due to the g factor.

The g factor represents what is common across an infinite universe of mental ability tasks. That is, performance across all mental tasks shares a common influence, namely, the g factor. Through these mental ability tasks g is called forth, which is manifested in test score performance. Because the g factor represents general intelligence, the measurement of g does not rely on any specific mental ability task. Instead, the g factor is best represented by performance across a breadth of diverse mental ability tasks.

Today there are various intelligence tests that are available to measure intelligence. These tests and their constituent tasks (i.e., subtests) may vary widely in their appearance or theory underlying them, but a composite derived from the tasks, called an IQ, for the most part measures g the same across the tests. In 1904, Charles Spearman coined the phrase “the indifference of the indicator” to describe this very phenomenon—the surface characteristics of the specific task are unimportant in measuring the g factor.

[Page 714]Although IQs across a variety of intelligence tests tend to measure the same amount of g, not every mental ability task within each intelligence test is an equal measure of g. For example, reasoning- or vocabulary-type tasks are better measures of g than tasks that require a person to repeat back a set of numbers. The more complexity involved in a mental ability task, the more of g is measured. Complex tasks generally require more mental manipulation or information processing. A composite summarizing scores from a variety of mental ability tasks tends to measure a similar—though not identical—amount of g as does another composite summarizing scores from a different set of mental ability tasks. But a single mental ability task may vary quite substantially from another in how much g is measured in that task. All mental ability tasks measure g to some extent, but the IQs are the scores that mostly reflect g.

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