Via Tyler Cowen, a paper on what opens the amber door into the top one percent of Swedish society. Not sure about the precise methodology, IQ was seen as moot, with working class origin and extroversion emerging as more important (in opposite directions). Quick picks:
"We find a clear working class disadvantage... differences in educational attainment levels cause a large part of the gap, but less so over time... Differences in personality traits measured at around the age of 18 years also help explain the class origin differentials, and more so over time. The decomposition analyses indicate that the net effect of cognitive abilities is small..."