Other research has concluded that there is slightly larger variability in male scores in certain ares compared to female scores, which results in slightly more males than females in the top and bottom of the IQ distribution. The existence of differences between male and female performance on math-related tests is contested, and a meta-analysis focusing on gender differences in math performance found nearly identical performance for boys and girls. Currently, most IQ tests, including popular batteries such as the WAIS and the WISC-R, are constructed so that there are no overall score differences between females and males. While the concept of "race" is a social construct, discussions of a purported relationship between race and intelligence, as well as claims of genetic differences in intelligence along racial lines, have appeared in both popular science and academic research since the inception of IQ testing in the early 20th century. Despite the tremendous amount of research done on the topic, no scientific evidence has emerged that the average IQ scores of different population groups can be attributed to genetic differences between those groups. A 1996 task force investigation on intelligence sponsored by the American Psychological Association concluded that there were significant variations in IQ across races. However, a systematic analysis by William Dickens and James Flynn (2006) showed the gap between black and white Americans to have closed dramatically during the period between 1972 and 2002, suggesting that, in their words, the "constancy of the Black-White IQ gap is a myth." The problem of determining the causes underlying racial variation has been discussed at length as a classic question of "nature versus nurture", for instance by Alan S. Kaufman and Nathan Brody. Researchers such as statistician Bernie Devlin have argued that there are insufficient data to conclude that the black-white gap is due to genetic influences. Dickens and Flynn argued more positively that their results refute the possibility of a genetic origin, concluding that "the environment has been responsible" for observed differences. A review article published in 2012 by leading scholars on human intelligence reached a similar conclusion, after reviewing the prior research literature, that group differences in IQ are best understood as environmental in origin. More recently, geneticist and neuroscientist Kevin Mitchell has argued, on the basis of basic principles of population genetics, that "systematic genetic differences in intelligence between large, ancient populations" are "inherently and deeply implausible". The effects of stereotype threat have been proposed as an explanation for differences in IQ test performance between racial groups, as have issues related to cultural difference and access to education. In the United States, certain public policies and laws regarding military service, education, public benefits, capital punishment, and employment incorporate an individual's IQ into their decisions.