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> I'll go back when it's safe, but not before then. BART is already exceedingly safe. Even with robberies rising 45% this year the overall robbery rate is proj

> I'll go back when it's safe, but not before then. BART is already exceedingly safe. Even with robberies rising 45% this year the overall robbery rate is projected to be 1.7 per million trips[1]. To put it another way, if every time you rode the BART you also bought a CA lottery scratch-card you'd be about as likely to get robbed as you would to win the jackpot (normalized odds for a $2 scratch card: 0.00000167[2], normalized odds for robbery 0.0000017). Do I think BART is a great system? Absolutely not. Do I prefer taking a Lyft to the airport rather than the BART? Yes. But I've worked in cities with unsafe public transit systems, and the BART simply doesn't compare. [1]: http://www.sfgate.com/crime/article/Crime-stats-show-where-surge-in-BART-robberies-is-11108092.php http://www.sfgate.com/crime/article/Crime-stats-show-where-s... [2]: http://www.calottery.com/LotteryHome/play/scratchers-games/$3-scratchers/wild-bingo-1254 http://www.calottery.com/LotteryHome/play/scratchers-games/$...

topynate 9y ago
That's interesting, because it is quite improbable that someone would "know personally" several lottery winners at ~590000 to 1 odds, even if his acquaintances routinely bought two tickets a day. GP's post is just a single datum, of course, but it's enough in itself to raise doubt about the accuracy of that 1.7/megatrip statistic. Numerically, suppose GP knows 30 people who make 600 trips on BART each year. In one year, the chance of at least one robbery in that group, given the quoted odds, is three percent. The chance of multiple robberies, i.e. at least two, is under 0.05 percent – over 2000 to 1 odds against. Even over a ten year period, the odds are 25 to 1 against. If GP's personal experience is not unusual, then something is screwy with the stat.
- thaumasiotes 9y ago
  > GP's post is just a single datum, of course, but it's enough in itself to raise doubt about the accuracy of that 1.7/megatrip statistic. In itself it's not that great. You have two obvious options: 1. Robberies on BART are generally not reported. You'd need a very high rate of nonreporting to mess with the conclusion that overall BART trips are quite safe. 2. Certain BART trips, by location, time of day, or some other metric, are much more dangerous than the average, and the BART-using public preferentially avoids taking those trips. If you believe in case 2, it's not at all surprising that someone might know several people who have been robbed on BART. You'd conclude that their social circle has atypical BART habits. How many robberies-at-gunpoint do you think occur in the packed rush hour trains?

topynate 9y ago

That's interesting, because it is quite improbable that someone would "know personally" several lottery winners at ~590000 to 1 odds, even if his acquaintances routinely bought two tickets a day. GP's post is just a single datum, of course, but it's enough in itself to raise doubt about the accuracy of that 1.7/megatrip statistic. Numerically, suppose GP knows 30 people who make 600 trips on BART each year. In one year, the chance of at least one robbery in that group, given the quoted odds, is three percent. The chance of multiple robberies, i.e. at least two, is under 0.05 percent – over 2000 to 1 odds against. Even over a ten year period, the odds are 25 to 1 against. If GP's personal experience is not unusual, then something is screwy with the stat.

thaumasiotes 9y ago
> GP's post is just a single datum, of course, but it's enough in itself to raise doubt about the accuracy of that 1.7/megatrip statistic. In itself it's not that great. You have two obvious options: 1. Robberies on BART are generally not reported. You'd need a very high rate of nonreporting to mess with the conclusion that overall BART trips are quite safe. 2. Certain BART trips, by location, time of day, or some other metric, are much more dangerous than the average, and the BART-using public preferentially avoids taking those trips. If you believe in case 2, it's not at all surprising that someone might know several people who have been robbed on BART. You'd conclude that their social circle has atypical BART habits. How many robberies-at-gunpoint do you think occur in the packed rush hour trains?