general intelligence

Meaning: Charles Spearman proposed that a single general factor, g, underlies performance across mental tasks. He saw that scores on verbal, spatial, and reasoning tests correlate positively and used factor analysis to extract the shared factor. In his two-factor theory, each test also taps a specific ability (s) unique to that task. Cattell later divided g into fluid intelligence (reasoning in novel problems) and crystallized intelligence (accumulated knowledge and skills). Fluid ability tends to decline with age, while crystallized ability tends to hold steady or grow.

On the MCAT: A passage may describe test scores that all load onto one factor, which supports g, or it may ask you to match a description to a theory. The usual contrast is with theories that treat intelligence as several relatively separate abilities. Gardner's multiple intelligences include linguistic, logical-mathematical, musical, spatial, bodily-kinesthetic, interpersonal, intrapersonal, and naturalistic. Sternberg's triarchic theory lists analytical, creative, and practical intelligence. IQ tests are commonly treated as measures of g.

Common confusion: g does not mean a person is equally skilled at everything. It means abilities are positively correlated across many people, so someone who scores high on one test tends to score higher on others. It is a statistical construct drawn from those correlations, and the specific abilities (s) still vary.