How to increase your earnings; read more non-fiction

I came across an interesting statistic in an Institute of Management Accountants (IMA) publication:

People who read seven non-fiction books a year earn more than twice as much money as people who read only one.
Non-fiction includes biography, history, self-help or business books.

 Okay I read probably twenty non-fiction books a year and I certainly don’t think I make twice as much as people who only read one; maybe it’s all those memoirs…