That would take another study. However, I would caution you to come to the conclusion that simply working harder will make you successful. This false idea is proposed by a lot of 'feel-good' motivational speakers. It can be a contributing factor, but will be one in a multi-variate explanation.
As an example, Warren Buffet is a multi-millionaire but he does not work millions of times harder than somebody from the ghetto who makes a fraction of what he does.
The 'work ethic' programming is used to brainwash people in many ways as is the 'be positive' programming which suspends critical thought and makes people more susceptible to sales tactics.
cityboy12,
This is correct. Working hard is a contributing factor that leads to goals accomplishment.
Having access to quality material, quality mentors/teachers, and working smart are also contributing factor.
For example, I bought a trading system 2 years ago and work really hard to follow the rules of the trading systems and still loss money after xx trades. Why did I lose money, because I failed to prove to myself that the system had proven historical success. I did not work smart.