Traditionally, research on "g" has concentrated on psychometric investigations of test data, with a special emphasis on factor analytic approaches. However, empirical research on the nature of "g" has also drawn upon experimental cognitive psychology and mental chronometry, brain anatomy and physiology, quantitative and molecular genetics, and primate evolution. Some scientists consider "g" as a statistical regularity and uncontroversial, and a general cognitive factor appears in data collected from people in nearly every human culture. Yet, there is no consensus as to what causes the positive correlations between tests.