Simpson’s paradox. If we compare average 2003 National Assessment of Educational Progress mathematics scores, we find that eighth-grade students in Nebraska do better than eighth-grade students in New Jersey. But if we look only at white students, New Jersey does better. If we look only at minority students, New Jersey again does better. That’s Simpson’s paradox:

the comparison reverses when we lump all students together. Explain carefully why this makes sense, using the fact that a much higher percentage of Nebraska eighth-graders are white.