Well, at least one of the articles seems to imply that the first officer retracted the gear because she happened to be thinking about retracting the gear, sort of "automatically", without being asked by the PF to retract the gear. And goes on to describe it as a "known psychological phenomenon".
They then claim the early gear retraction lead to "the tail hitting the runway", which caused the PF to abort. I'm reading elsewhere the Q400 only has Weight-on-Wheels sensor on the nose gear, is that true?
Edited:
Another article claims the gear retracted 3 seconds before the aircraft would have achieved VR.
http://www.tageblatt.lu/nachrichten/...h-ein-22371399