Differences in "g" between racial and ethnic groups have been found, particularly in the U.S. between black- and white-identifying test takers, though these differences appear to have diminished significantly over time, and to be attributable to environmental (rather than genetic) causes. Some researchers have suggested that the magnitude of the black-white gap in cognitive test results is dependent on the magnitude of the test's "g" loading, with tests showing higher "g" loading producing larger gaps (see Spearman's hypothesis), while others have criticized this view as methodologically unfounded. Still others have noted that despite the increasing "g" loading of IQ test batteries over time, the performance gap between racial groups continues to diminish. Comparative analysis has shown that while a gap of approximately 1.1 standard deviation in mean IQ (around 16 points) between white and black Americans existed in the late 1960s, between 1972 and 2002 black Americans gained between 4 and 7 IQ points relative to non-Hispanic Whites, and that "the "g" gap between Blacks and Whites declined virtually in tandem with the IQ gap." In contrast, Americans of East Asian descent generally slightly outscore white Americans. It has been claimed that racial and ethnic differences similar to those found in the U.S. can be observed globally, but the significance, methodological grounding, and truth of such claims have all been disputed.