data: Creating Leaders

HBR (Harvard Business Review) is in business of business,
and here they presents statistically sound method to select and grow business leaders.
Interesting... likely it apply to other levels of organizations.
There are sound criteria for making decisions about promotions (below),
rather than typical observed level of ambition of potential candidates.

Why More CEOs Should Be Hired from Within

"... typical large American firm would, for example, hire a CEO from outside about 30 percent of the 
times. And there is some research that I believe in that shows that they should only be doing that on average six percent of the time. So, five times less. It is so much better to promote someone from within if you have the right type of candidate
...
typically have people from the top three levels—so, it’s CEO and the next three levels—that about 9 percent of them have the potential to become very successful CEOs. Now, what happens is this: if you only look at the next level, at the direct reports of the CEO, that’s typically about 8 people. So, you know, 9 percent of 8 people gives you 0.7 internal candidates, which explains why in the other 30 percent of the times they go outside
...
 you should do is start your CEO succession...three years before."

Fernández-Aráoz is the co-author of the new HBR article
“Turning Potential into Success: The Missing Link in Leadership Development.”