On balance of evidence, The Doctor has:
no control over his regenerations
some control over his regeneration
total control over his regenerations
Romana and possibly River have some control over how they turn out. Is this
typical for Time Lords or Ladies
typical only for Time Ladies
unusual for Time Lords or Ladies
I've seen arguments about regeneration that start from very different assumptions from mine, so I post a poll to see how widespread they are.
We have seen Romana, River, the Master and the Doctor regenerate.
Romana tried a few bodies on for size before settling on the one she wanted, which was an exact copy of someone else. Conclusion: A Lot of Control.
River concentrated on a dress size and seemed happy with the result. Conclusion: maybe some control.
The Doctor, however...
9th Doctor: I might never make sense again! I might have two heads, or no head. Imagine me with no head, ha! And don't say that's an improvement... But it's a bit dodgy, this process. You never know what you're going to end up with.
So I don't figure he has control. Two was offered choices of who he'd look like next but didn't get to decide for himself, and was very cross about it. Everyone seems to need a mirror to get to know their new selves. 11 didn't recognise himself and thought he looked a bit rubbish. I've always thought of regeneration as something that happens to him, not something he does.
So, which do you reckon?
Also, I know since The Corsair we know for certain Time Lords can be male or female when they regenerate, so I don't see how there'd be a difference in regeneration ability, but with only the handful of data points *big shrug*.
It's only the Doctor we've really seen go through a life cycle. And the Doctor, according to the Doctor, even if we'd rather ignore him, is half human. Others from Gallifrey could therefore differ from the Doctor quite a lot.
Actually if there's one thing we know about the Doctor it's that he's very thoroughly atypical.