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Comment by pedvide | Hacker News Reader

That depends on what your hypothesis is. If it is that Waymo cars are safer than for-hire (which I guess it's what Waymo claims), then you need enough data to reject the null hypothesis that they are equally safe. Right now there doesn't seem to be enough data to do this, so you can't conclude they are safer. They could be equally safe or more dangerous.

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But how do you conclude then that they are less safe? They are neither proven to be more, less, or equally safe. So any statement of "more injuries" is as unfounded as "less injuries" or "just as many injuries".

That seems like the same statement, unless we apply stochastic class level subtlety.

If a driver doesn't get into a crash after a single mile, you can't conclude that they are safer than the average driver. If a driver does get involved in a crash after a single mile, it's very likely that they are not safer than the average driver. It could of course be extraordinarily bad luck, but that's unlikely.

> If a driver does get involved in a crash after a single mile, it's very likely that they are not safer than the average driver. It could of course be extraordinarily bad luck, but that's unlikely.

This is not that simple. Emergency service vehicles are at a very high risk of collision when they pull out of the station and crossings close to the station, or when leaving a situation under time pressure. Busses are at an increased risk of collision when pulling away from a bus stop. Construction vehicles are at a high risk of collision when they pull away from a construction site at a busy road.

Hence why you need more data, after which average accidents per mile are a much stronger indicator.

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