I'm trying to get my company to understand the value of developing an internal training program that would develop potential managers from within. Although I can find multiple sources of information on how to train and develop, I'd like some statistical information on the comparison of training for internal managers as opposed to external hiring. Is there a topic on this one? Thanks.

Reach Out To ASTD
The American Society for Training & Development might be a good place to start. Or, if you're in another country, there might be a similar organization. In addition to surfing their web site, you might find out where the nearest chapter is and contact one of their officers to see if they could answer your question.
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If you get anything good with that, let us know back here, I would certainly be interested to know as well!