It is pretty well established that folded dipoles have much greater acceptable-SWR bandwidth than ordinary dipoles.
Radiation efficiency is simply the quotient of radiated power to the antenna feedpoint input power.
Seeing that folded dipoles are able to achieve the greater bandwidth without introducing a designed-as-lossy element (a technique not unheard of with large-bandwidth antennas), what is the effect on radiation efficiency of using a folded dipole as opposed to a regular dipole? Are there any considerations affecting folded dipoles that would not affect a regular dipole antenna erected in the same physical location which would have a noticable impact on the radiation efficiency?
For the purpose of this question, assume otherwise identical conditions; identical height over ground, identical ground, identical possible parasitic elements, identical feedline, etc. Also, note that I am not asking about the radiation pattern of the folded dipole; I am only concerned with the antenna's radiation efficiency here, unless some other factor has a noticable impact on the radiation efficiency as compared to a regular dipole.
A great answer would look at this from both the perspective of a same-wire-length antenna (meaning approximately double the folded dipole's physical length) as well as a same-physical-space antenna (meaning effectively half the radiator length).