• ImplyingImplications@lemmy.ca
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    9 months ago

    Humans are bad at statistics and probability. We’re naturally wired to find patterns and connections and make decisions quickly without needing to perform calculations. It works for simple stuff but when things get a little complicated our “gut feeling” tends to be wrong.

    My other favourite probability paradox is the Monty Hall Problem. You’re given the option to pick from 3 doors. Behind 2 of them are goats and behind 1 is a new car. You pick door #1. You’re asked if you’re sure or if you’d rather switch doors. Whether you stay or switch makes no difference. You have a 33% chance of winning either way. Then you’re told that behind door #2 there is a goat. Do you stay with door #1 or switch to door #3? Switching to door #3 improves your odds of winning to 66%. It’s a classic example of how additional information can be used to recalculate odds and it’s how things like card counting work.

    • Iamdanno@lemmynsfw.com
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      9 months ago

      After you find out there’s a goat behind door #2, you have a 50% chance whether you stay on 1 or move to three. There are only two possible outcomes at that point (car or goat), so either way it’s a coin flip.

      • Feathercrown@lemmy.world
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        9 months ago

        You’re wrong, but you’re in good company. It’s a very counterintuitive effect. One technique that can be helpful for understanding probability problems is to take them to the extreme. Let’s increase the number of doors to 100. One has a car, 99 have goats. You choose a door, with a 1% chance of having picked the car. The host then opens 98 other doors, all of which have goats behind them. You now have a choice: the door you chose originally, with a 1% chance of a car… or the other door, with a 99% chance of a car.

        • june@lemmy.world
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          9 months ago

          Oh that’s so weird. I get it from a proof perspective but it feels very wrong.

          My brain tells me it’s two separate scenarios where the first choice was 99:1 and after eliminating 98 there’s a new equation that makes it 50:50.

          • Jojo@lemm.ee
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            9 months ago

            The important thing is that the host will always show you a goat, meaning the only way the other door has another goat is if you just so happened to pick the car the first time.

            Take the situation to the extreme and imagine a hundred doors, and after you pick a door, the host opens 98 doors, all of them with goats behind them. Now which seems more likely, that you chose right the first time, or that the other door has the car?

          • Iamdanno@lemmynsfw.com
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            9 months ago

            Now you have 2 choices: the door you chose, or the only other door left. One has a goat and one has a car. That’s fifty-fifty.

            In your explanation, the door originally had a 1% chance, but after showing 98 goats, it has a 50% chance.

            • june@lemmy.world
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              9 months ago

              No. Taking it to the extreme with 100 doors, your first pick was a 1% chance to get the car. The host then shows you 98 other doors that all have goats.

              What’s more likely? That you picked the right door when it was 100:1? Or that the other door is the one with the car?

            • Jojo@lemm.ee
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              9 months ago

              The important thing is that the host will always show you a goat, meaning the only way the other door has another goat is if you just so happened to pick the car the first time.

              Take the situation to the extreme and imagine a hundred doors, and after you pick a door, the host opens 98 doors, all of them with goats behind them. Now which seems more likely, that you chose right the first time, or that the other door has the car?

              • Iamdanno@lemmynsfw.com
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                9 months ago

                The host’s intentions are irrelevant. Numerically, there are only two choices. That makes it fifty-fifty.

                • Jojo@lemm.ee
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                  9 months ago

                  You think that even in the hundred-door case? Test it. Hell, even test it in the 3 door case. It is empirically not 50%.

                  If the host had an even chance to show you either door, you’d be right, but since the host always shows you a goat, the two events (picking a door and choosing whether to switch) are no longer independent, since if you pick a goat it forces the host to pick the other goat.

      • Hellnikko@lemmy.world
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        9 months ago

        You’re incorrect. It is indeed a higher chance to switch from #1 to #3. You should look up Monty Hall paradox. It’s in the link that you replied to that explains it.

        • Jojo@lemm.ee
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          9 months ago

          The important thing is that the host will always show you a goat, meaning the only way the other door has another goat is if you just so happened to pick the car the first time.

          Take the situation to the extreme and imagine a hundred doors, and after you pick a door, the host opens 98 doors, all of them with goats behind them. Now which seems more likely, that you chose right the first time, or that the other door has the car?