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by shash16 hours ago |
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upvoteby the__alchemist9 hours ago|
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Your point is fair and and important distinction. I think when estimating a risk factor though, this empirical data, while a low sample size, is a valuable statistic because it's empirical, and not that small of a sample size. Maybe going forward, we have 3 risk levels:

  - Historical. Low N as you say. (Even though each mission and spacecraft is different and they're spread out over time, there's value in this)
  - Bureaucrat number; absurdly low, but looks good to politicians etc
  - Engineering estimate
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upvoteby shash6 hours ago|
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Yes. It provides a prior for Bayesian analysis if nothing else.
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upvoteby stetrain16 hours ago|
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So the risk factor for Apollo could have actually been 1/1000 but they were just really unlucky?
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upvoteby shash6 hours ago|
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Yes, actually. This is similar to having a 100 year flood five years in a row. It doesn’t mean that the flood occurs only once in 100 years. _On average_ it’s 1/100 probability of occurring in any given year.

But then, Apollo 1 was after all the first mission on the Saturn V. I think we should assess even its pre-launch risk much higher than the rest of them. Similarly Artemis II has a much higher risk than the subsequent ones will have.

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upvoteby stetrain5 hours ago|
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But we’re talking about the risk of a defined set of events that have concluded, not a prediction of the future.

Of course Apollo would have likely had a better average if it had continued, but the risk of the Apollo program, as executed, included things like the first flight of the Saturn V.

If the final empirical mortality result of the Artemis program is 1/30 or less, it will be better than Apollo in that statistic.

A comparison of acceptable mortality is where this discussion began. If Apollo was acceptable at 1/12 (We did it, it was apparently acceptable as the program was not cancelled due to mortality rate) then an acceptable mortality of 1/30 is stronger than Apollo, not weaker.

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upvoteby d1sxeyes10 hours ago|
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If I toss a coin four times and it comes up heads three and tails once, it doesn’t mean that there’s a 75% chance that this coin lands heads up. Be careful about conflating risk factor and mortality rate.
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upvoteby stetrain5 hours ago|
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> If I toss a coin four times and it comes up heads three and tails once, it doesn’t mean that there’s a 75% chance that this coin lands heads up.

No, but it means that to ensure that I do better on my next set of coin tosses I need to beat 3 in 4, not 1 in 2.

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upvoteby d1sxeyes5 hours ago|
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But you doing better is independent of the risk involved. The chances of you getting 3/4 heads or better is around 31%, so theres ~69% chance you’ll do worse next time round. Doesn’t change the fact that each coin toss is still 50/50.
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upvoteby jjk1663 hours ago|
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> Doesn’t change the fact that each coin toss is still 50/50.

That assumes a fair coin. The fact is you don't know what the odds were of getting heads or tails for that particular coin, all you know is that you got 3/4 heads. And in this analogy, a few hundred coins have every been made, in maybe a dozen styles, none of which have been fair, so you have no good reason to believe that this particular coin should have 50/50 odds of landing heads up.

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