I would suggest that an answer to "what do you think the percentage of employees who have stolen.." is a proxy question for, "just exactly how socially unacceptable to you is stealing from your employer"? It relates to, basically, your own levels of altruism, and what you perceive the local altruism levels to be. If you see that everyone around you is being altruistic, you feel a basic urge to keep the clean environment up, while if everyone around you is cheating, then you are less likely to keep up your own altruism.

I've had my bike stolen a few times. After getting a particularly nice bike stolen, I now am always on the lookout for unlocked bikes, and when I see one, the urge is most definitely there to grab it - 'retribution', if you will, for my own stolen bike. I don't go through with it, but the possibility is a lot more present in my mind than if I had never had a bike stolen from me.