How common was death in the arena?

[Epictetus]

...that gladiators of 1 BC had a 9:1 chances to live, the gladiators who lost - 4:1. 200 years later the gladiators had 4:1 chances to live, for those who lost - 1:1. The encreasing number of deaths on arena was probably caused by reduction of combats ...

This is interesting. If a fee had to be paid for each death, and the number of combats decreased over time, I would assume that there would be less a chance of death in the arena in the later centuries. Each gladiator would be more valuable, and each death would be more expensive, presumably, and the organisers would want to keep them alive to fight again.