Ron Garret wrote:
In article ,
"Peter Duniho" wrote:


"Ron Garret" wrote in message
...

[...]
I just did, but here it is again: if you believe that the risk of an
engine failure on any particular flight is P1 and you are willing to
accept a lifetime risk of experiencing an engine failure at no more than
P2, then you can use these two numbers and the formula for cumulative
probability to solve for N. You can then choose to stop flying after N
flights.

But making that choice is only useful, and only based on correct
information, if you make the choice prior to the first of N flights.

As I said, no one ever does that.


Not so. But it's pointless to argue with you and life is short.

rg

Okay, I haven't been following this thread much, but reading a few of
these, I think a number of posters are having serious problems with
probability. The posts by Peter Duniho that I've read, in contrast, do
seem to understand probabilistic reasoning.

Yes, someone could decide to limit their lifetime risk of an engine
failure to P2 by flying exactly N flights. But in real life such a
decision would be insane.

First, if you were to have an engine failure during those N flights, it
would almost certainly not occur on the Nth flight. Therefore people who
have an engine failure are extremely unlikely to ever reach N flights.

Second, for any real world value of N (say N=1000), the marginal
increase in risk for flying N+1 flights would be trivial. P2 is much,
much larger than P1. So having accepted the risk of flying 1000 flights
and having successfully completed them, to decide to stop flying just so
as to avoid passing some given lifetime P2 would be bonkers. Flying that
N+1 flight has a risk of P1, a tiny risk compared to the one the person
accepted (P2) in flying N flights.

--
David Rind