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Iminlesbian t1_ja9d89h wrote

Reply to comment by PM_ur_Rump in ELI5: why does/doesn’t probability increase when done multiple times? by Reason-Local

But what are the chances that two different planes will crash at the same airport in one day?

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Aussie_Scientist t1_ja9i88s wrote

Very low. Once one plane has crashed they’re likely to close the airport. If there are no planes taking off or landing, the only way for a second crash to occur is a plane falling out of the sky directly at the airport.

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Iminlesbian t1_ja9idsr wrote

Nah but ignoring all that.

Like say it crashed but the after effects weren't taken into account.

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PM_ur_Rump t1_ja9e0fb wrote

Barring outside influences, and assuming the odds are static, like dice, exactly the same as one plane crashing there, once one already has.

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Iminlesbian t1_ja9i0us wrote

But not before right?

I'm not arguing, this just always kind of messes up my head.

Like the changes of me winning two lottery being the same because the chances of winning the lottery are the same for each ticket.

But how likely is it that someone who plays the lottery all of their life wins, and how likely is it that they win twice?

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PM_ur_Rump t1_ja9kw7z wrote

The odds that they win twice in a lifetime is much more unlikely than the odds they win once.

But after they won once, the odds of winning again are exactly the same as if they had never won.

Think of the dice example. There is a one in six chance of rolling a specific number. Rolling again, there is still a one in six chance of rolling that same number. The number of sides hasn't changed, the number you chose didn't magically disappear.

The odds only change if you bet that you will roll two in a row before the first roll, because you are now betting on both events before they happen, not on a single event happening. The events themselves have no influence on each other.

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Iminlesbian t1_ja9lehu wrote

Ah I get it, thanks a lot. The lottery chances "resetting" after the first win actually makes sense to me.

I think that's where my head gets confused. If I saw a plane crash I'd think of it as "well there's no chance of two of that thing happening today!" Rather than " it's still just as likely to happen today."

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PM_ur_Rump t1_ja9mk20 wrote

Glad I could help ya figure something out! It's definitely a bit counterintuitive at first, and I once had the same confusion. Cheers!

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SYLOH t1_jaav09w wrote

Do note. The guy seems to be talking about simple odds using real plane crashes for some reason.
Real world statistics do not work that way.

In the real world plane crashes are not independent events.
In the real world you knowledge of the odds of plane crashes is not complete.
A plane crash will cause the ground crew and flight crew to change their behavior, shifting the odds.
A plane crash is evidence that your assumptions on the safety of a given model of plane might be incorrect.

In the magical world of simple odds, safety audits and groundings wouldn't make a lick of sense. They do in the real world.

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