Complex sentence: The Nobel Prize winning economist James Heckman writes that two assumptions made in the book are questionable: that "g" accounts for correlation across test scores and performance in society, and that "g" cannot be manipulated.
Split into simpler sentences: The Nobel Prize winning economist James Heckman writes that two assumptions made in the book are questionable. That "g" accounts for correlation across test scores and performance in society and that "g" cannot be manipulated.