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> It took me over 27 years, or about 10,000 days, to get robbed. That’s still a 1 in 10,000 probability. Pretty good.

No, no, no. That is not how probability works. That's like saying that if I live to be 100, the probability of me dying was 1 in 36,525.



Can you elaborate more? I would have thought your example isn't comparable, in that we death is inevitable, but being robbed isn't (as much, depending on circumstances)


An event happening only reveals that p > 0.

Imagine you have a giant 10000-sided dice. You throw that dice once every day searching for a magic number (e.g. 1337). "Hitting 1337" is an experiment with a binary outcome (yes/no).

On day 500 you hit the magic number. Did you have a 1 in 500 chance of hitting it? No, you had 1/10000 chance of hitting! Even if you throw it 10000 times, there's no 100% chance of hitting 1337 since the dice is still 10000-sided even after you hit any number (this is called "no replacement") so you can have, for example, 1338 coming twice and 1337 none. There is never a 100% probability (but it approaches 1 rapidly near 10000).

On the other hand, you can calculate the probability of "hitting 1337 at least once in N throws", which is actually the CDF of a binomial distribution[1], but you need the initial probability of a single event!

Bringing back the robbery theme, living a day of your life is just repeating the "being robbed today" experiment (throwing the dice) once a day. Being robbed on day N of your life just means you repeated the experiment N days and N-1 times the outcome was "no" and then a single "yes". This does not mean that the CDF was 1 at N attempts, it just means that it was greater than 0... and this is just the probability of "being robbed after N days", i.e., the CDF of "being robbed today", not the probability of being robbed itself.

Also: you can't evaluate probability a posteriori unless the events are repeatable under controlled conditions, in which case you repeat the experiment lots of times and derive the probability from the outcomes. Burglaries are not repeatable under controlled conditions!

[1] https://en.wikipedia.org/wiki/Binomial_distribution#Cumulati...


Maybe more accurate to say the probability of being robbed on a single day is 1 in 10,000? So on average he could expect to be robbed two more times in his lifetime.


just because your experience was 1/10000 doesnt mean your true risk is 1/10000 . You could have tossed 9999 heads and 1 tails, there's still a 50/50 chance on the coin... Similarly you could be overstating your risk..


The probability to get 9999 heads and 1 tail is so small that you have more chance of finding an unicorn in a forest. I'd toss that coin :-P


So you're saying unicorns exist? Because that coin toss could happen. Not sure if finding a unicorn in a forest could happen, unless unicorns exist ;)


Yes, I say that it's more likely to find an unicorn somewhere on Earth (an undiscovered species) than to get that toss sequence. We say that an event is impossible for _way_ less probabilities (I could be hit by a cosmic radiation and start to grow a third arm, but it's unlikely enough to say that it's impossible).




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