Blacks have extremely low visual memory so it is very difficult for them to recall digits in reverse Race and intelligence explanations Spearman s hypothesis IQ tests contain one or more sets of test questions of different varieties Individually administered tests often are composed of subtests that have different homogeneous item contents The mean Black White difference varies considerably across tests with different contents For example the BW gap is larger on tests that require the recall of a series of digits in reverse order than on tests that require the recall of a series of digits in forward order Across a large number of test the standardized mean Black White gap varies from near zero to over one standard deviation According to this variation between tests in the size of the standardized mean W B difference is not explainable in terms of test bias or in terms of differences in types of item content or other formal or superficial characteristics of the tests The g based factor hierarchy is the most widely accepted current view of the structure of abilities Correlations between an IQ subtest s g loading and the magnitude of the Black White East Asian score gap for that subtest pp 47 8 pp 138 9 For example the Black White gap is greater on backward digits span a test where subjects repeat digits in the reverse order that they are given and the more g loaded test than forward digits span a test where subjects repeat digits in the same order that they are given and the less g loaded test As predicted by Spearman s hypothesis the B W gap is largest on the most g loaded tests Narrowing of the B W gap has been seen mostly on less g loaded tests such as literacy tests Murray C 2005 The Inequality Taboo Commentary Magazine September 2005 Arthur Jensen argues that there is no independent evidence that the environmental explanations commonly given for the Black White gap for example past history of slavery discrimination caste status peer pressure against acting white etc have an effect on g p 510 The author of multiple factor analysis L L Thurstone 1947 warned we must guard against the simple but common error of merely taking a first centroid factor a first principal component or other mean factor in a test battery and then calling it a general factor Spearman s g then is a statistical artifact C Loring Brace 2001 The gap is larger to recall digits in reverse because blacks are much lower in visual intelligence a test where subjects repeat digits in the reverse order that they are given and the more g loaded test IQ tests are biased against blacks because they are designed to test people with high visualspatial intelligence This is obviously original research but I can not find no sources that supports my argument even though I am not black