A 2013 analysis of the National Assessment of Educational Progress found that from 1971 to 2008, the size of the black-white IQ gap in the United States decreased from 16.33 to 9.94 IQ points. It has also concluded however that, while IQ means are continuing to rise in all ethnic groups, this growth is occurring more slowly among 17-year-old students than among younger students and the black-white IQ gap is no longer narrowing. As of 2008, a study published in 2013 by Heiner Rindermann, Stefan Pinchelmann, and James Thompson have estimated the IQ means of 17-year-old black, white, and Hispanic students to range respectively from 90.45-94.15, 102.29-104.57 and 92.30-95.90 points. They explain that the gap may persist due to the crack epidemic, the degradation of African-American family structure, the rise of fraud in the educational system (especially with respect to No Child Left Behind), the decrease in unskilled real wages and employment among African-Americans due to globalization and minimum wage increases, differences in parental practices (such as breastfeeding or reading to children), and "environmental conditions shaped by [African-Americans] themselves." To resolve this, they ultimately recommend the reestablishment of "meritoric principles" and "blindly graded objective central exams," as opposed to "affirmative action," in education.
Question: How many reasons are cited as causing the persistent gap between white and black IQs?
Answer: 6; 6