I don't know about the study, but in general, I wouldn't pay much attention to the news. They tend to take any information and distort it to suit a point of view, rather than just report a fact.
I feel as safe in Mexico as anywhere else. Sure, there are drug related crimes and murders. They also occur in many major US cities. As long as you don't go where the drug lords/gangs are holding their turf wars, there is no problem.
Two years ago I was in Jerusalem, and even went to Bethlehem on the West Bank. This was shortly after two Israelis had been gunned down in Tel Aviv. Seeing the news, I expected tight check points and a war ravaged West Bank. Reality was totally different. Both Jerusalem and Bethlehem were in great shape. There were less guards and people with guns than I see say in Germany or other European cities. Same in Mexico. There are guards patrolling, but not in great numbers.
It is probably easier to get caught in a terrorist incident in major European (or even American) cities than to be in trouble with a drug band in Mexico. They don't have any interest in tourists or destroying the livelihood of the locals, whereas terrorists are truly targeting innocent people. As mentioned before, most of the violence in Mexico that you hear about is not directed at foreigners, and it tends to be exaggerated to get people to buy newspapers or click through stories on the web.
