Why has wage inequality risen?

Wage inequality has increased in many economies in recent decades. Discuss the three leading hypotheses regarding the causes of this increase. What does the empirical evidence tell us about the quantitative importance of each of these factors?

The US economy has almost double since the 1970s, and labour productivity has risen over this period. Yet real wages for the median worker hasn’t changed much since the 1970s, and below-median male wages have fallen; showing that the increasing size of the economy hasn’t been fairly distributed.

The rise in inequality between high skilled and low skilled workers is particularly pronounced, with Autor finding that households which are composed of university education individuals earned $30,298 more than non-skilled workers in 1979, but this rose to $58,249 by 2012, an increase of 92%. [...]