on, word fluency, space, reasoning, and memory. Guilford may hold the record on distinguishing numbers of factors, which he defined in 1967 as the completion of a specific type of operation on a specific type of product with a specific type of content. He found five operations, six products, and four kinds of content, for a whopping 120 (5 x 6 x 4) factor total. Unfortunately, Horn & Knapp (1973; as cited in Mackintosh, 1998) applied his factorial procedures to his test data and found they supported randomly generated factorial theories just as well. Contemporary factor analysts generally cite nine different kinds of general mental ability: fluid reasoning (critical thinking ability), acculturation knowledge (breadth and depth of knowledge of the dominant culture), quantitative knowledge (mathematical ability), short-term memory (involving events in the last minute or so), long-term memory, spatial ability (measured in tasks such as comparing rotated objects for similarity), auditory processing (perception of sound patterns under distraction or distortion), processing speed (speed of response given an intellectually simple task), and correct decision speed (speed of response given an intellectually challenging task). Factor analysis is an incomplete solution to the problem of intelligence: while it describes relationships between different IQ tests, it cannot tell us much about the structure of human abilities. The existence of a general factor describing the correlation of IQ tests does not imply that it measures a cognitive process; it is quite possible that the tests measure any number of processes that happen to overlap, thus the various theories mentioned above.Genetic factorsHeritability of intelligence (or any other characteristic, for that matter) is the proportion of the total variation in the characteristic in a population that can be attributed to genetic differences between members of the population. Estimates of heritabilit...
