General intelligence

Charles Spearman (British psychologist, 1863–1945) described a concept he referred to as general intelligence or the "g factor". He utilized the method named 'factor analysis' to investigate a few mental ability tests; his conclusion was that the results and scores on these tests were very similar:

People who did well on one cognitive test usually performed well on other tests, while those who performed badly on one test usually scored badly on others. Spearman concluded that intelligence is a general cognitive ability that can be measured and numerically expressed.