I think you mean 1-1/e (~= 1 - (1-10^-6)^(10^6)). But yes, the idea that you can just divide a statistic sampled over thousands of events linearly to get a meaningful statistic for one occurrence of the event is ridiculous.

Yes, thank you.

Neither. 1/e would require that they all be independent random events which is not true in the general case (and mathematically 1/e would only be an approximation anyway). 1 would require that they be entirely dependent, which is also not true in the general case.

2 micromorts does not mean 2 separate risks, each of which has a 1 in 1 million chance of killing you. It means a single risk that has a 1 in 500 thousand chance of killing you. Similarly, it would be absurd to define 1 mort as the combination of 1 million separate risks, each of which has a 1 in 1 million chance of killing you. Whether 1 mort is guaranteed death or 1 - 1/e chance of death (my previous mention of it being 1/e was mistaken) is a property of how we define the unit to work, not a property of how correlated 1 million separate risks happen to be. Definitions that give answers other than 1 - 1/e or 1 don't make any sense.

> mathematically 1/e would only be an approximation anyway

If we're going with the definition that treats micromorts as independent, then it would make sense to define a mort as exactly a 1 - 1/e chance of death, and a micromort as a 1 - e^(-10^(-6)) chance of death, rather than a 10^-6 chance of death, but the difference is smaller than the degree of risk that we can measure or care about, so the difference is inconsequential, and it would still make sense to describe a micromort as a 10^-6 chance of death.