Motivational factors — they may be hard to keep data on (6)
I believe the answer is:
drives
I believe this clue is a double definition.
'motivational factors' is the first definition.
(eg factors driving behaviour)
'they may be hard to keep data on' is the second definition.
(as in hard drives)
(Other definitions for drives that I've seen before include "Drivers kinds of urges" , "Motors" , "Applies force to propel something" , "Controls movement of a vehicle" , "Operates a vehicle" .)