1. Suppose we did the odds of death from the shuttle after the first 50 shuttle flights. 1 failure out of 50 = 2%. If we did it after 100 flights, sure, it would be 1%, but we already have the second failure after only 13 flights into the second 100-flight cohort, so the shuttle better fly the next 87 missions without fatality or that percentage goes back up. Since it has been about 80 flights between crashes, that may or may not happen.
2. We could calculate it based on persons who have died as a percentage of those who have flown. This, in fact, might be the most useful statistic. Since Yuri Gagarin in 1961, approximately 400 different humans have attempted to fly into space. At least 17 died (I say "at least" because there are suspicions of unreported Cosmonaut deaths). 17 out of 400 is about 4%. That percentage would be higher if it were just US astronauts, btw. I saw an astronaut quote this figure on tv today, so it is not something I pulled out of the air but rather the kind of figure real-life prospective astronauts think about, however slightly, when signing that release.
3. We could look at the average time between major catastrophes. The three years are 1967, 1986 and 2003. A nineteen-year interval followed by a seventeen-year interval. While there were a lot more flights in the latter period, we also were much more technologically sophisticated and had learned from a lot of mistakes. That suggests that the odds of dieing as a function of time are staying about the same or even increasing.
My opinion from the facts is that boarding a government spacecraft for a spaceflight has a statistically significant death rate in the low single digits, around 2% and maybe higher. As long as the technologically obsolete Space Shuttle keeps flying, I doubt those odds will go down much no matter how many lessons NASA learns from each crash. I would make sure my life insurance were fully funded before boarding one of those ageing deathtraps.