Statistically it is very low. People that do not have an understanding of what parkour is, or think they know what it is without experiencing it, or think it is about jumping great heights and risking death are mistaken.
People that attempt parkour outside of their skill set, and have not trained their body and mind both physically and mentally to master even the simplest of parkour moves have no idea what they are doing.
Just because you see a person riding a unicycle while juggling, and it looks cool, doesn’t mean you can do it too. It took that person many, many hours of practice to develop those skills.
The same is true for parkour. I am surounded by traceurs that have far greater skill and ability than myself. I admire what they can do, and the work, training, and practice hours they have put into acquiring those skills. I would be a fool to even try to think I could do what they do without commiting myself to the same arderous training and practice, building and conditioning of my body to be at that level.
Parkour is about training at the level you are currently at. If you have only been training for a day, or a year, there is no way you will be able to do some of the things that someone that has been training for 8 years can do. Sure you might get lucky a few times on some things, but luck plays a very small part in parkour, and that is usually in the midst of a failure, or a mistake, or a slip on a patch of wet grass. As in that person was lucky their injuries were not worse. Parkour also builds up skills in the event of such failures, and those are also learned from the ground up. Not the other way around.
Jumping from building rooftops. Some people think that is what parkour is. It isn’t that at all. Some people can and do jump from rooftops, but they won’t be doing it for very long. That type of impact wreaks havoc on the ankle, knee and hip joints. It also puts undue pressure and compression on the spine. After a while, it will even be difficult for those people to walk without pain, much less practice parkour.
One of the underlying philosophies in parkour is the ability to be strong and useful in order to serve others. It has part of its origins in the fire brigade in which David Belle’s father served. He wanted to be strong, and agile to be able to do his job to the best of his ability in order to serve the people and effect rescues, which he did.
You can’t do any of that (be strong, useful and serve the people) if you can’t walk, or you are dead because you didn’t understand the underlying nature and systematic training and conditioning parkour provides, and requires.
Find a certified instructor, find a gym. Find a place that teaches beginners, and focuses on safety and the basics. A gym and/or instructor that can modify training based on the needs, skills and abilities of each person learning parkour for the first time. Start small, and work your way up all the while within your range of abilities. Understand your own limitations, the human body and simple physics.
Train smart, not crazy.