Intelligence is important, but intelligence without effort is sometimes wasted.

Nobel Prize-winning economist James Heckman likes to ask people how great a role innate intelligence plays in financial success. Like how much the difference between my income and yours, for example, is based on our relative IQs.

Most people say about 25 percent. Some go as high as 50 percent. (For a long time, I would have guessed even more.)

But Heckman's research reveals something else entirely. Innate intelligence plays, at best, a 1 to 2 percent role in a child's future success.

Instead, financial success is correlated with conscientiousness: self-discipline, perseverance, and diligence.

That comes as no surprise to people familiar with research on married couples: People with relatively prudent and reliable partners tend to perform better at work, earning more promotions, making more money, and feeling more satisfied with their jobs.

"Partner conscientiousness" (for men and women) predicts future job satisfaction, income, and likelihood of promotion.

According to the researchers, "conscientious" partners perform more household tasks, exhibit more pragmatic behaviors that their spouses are likely to emulate, and promote a more satisfying home life, all of which enables their spouse to focus more on work.

As one researcher said, "These results demonstrate that the dispositional characteristics of the person one marries influence important aspects of one's professional life."

In non-research-speak, a good partner sets a good example, and makes it possible for you to be a better you.

Granted, luck also plays a major role in success. As the researchers write, "The maximum success never coincides with the maximum talent, and vice versa. Our simulation clearly shows that such a factor is just pure luck."

But you can't control luck. And you can only partly control IQ. While you can certainly become more educated, fluid intelligence -- the ability to think logically and solve problems independent of acquired knowledge -- is somewhat trainable but tends to be largely fixed. 

But what you can control is how conscientuous you are. How diligent you are. How persistent you are.

Everyone defines success differently, as well they should. But if you happen to define success by traditional measures, like professional achievement or fortune or fame, hard work is the great equalizer.

You may not be smarter than everyone else. You may not be as talented. You may not have the same great connections, the same great environment, or the same great education.

You may have none of those things.

But you can substitute effort for intelligence -- because, over time, effort results in skill and experience. You can always be more persistent than others. You can always be more disciplined.

And that, science says, will have the biggest impact on your pursuit of success.

Inc