So first of all, the probability of getting struck by lightning ***today*** is not 1 in a million – it’s much less. Humans live for about 27,000 days (conservative estimate – that’s 75 years). This means that if, each day, you had a chance of getting struck by lightning of 1 in a million, your odds of getting struck some time in your life would be about 1 in 37 (you can calculate this as 1-(1-1/1,000,000)^(27,000)). With those kinds of odds, we’d all personally know several people who had been struck by lightning.
The 1 in a million odds instead apply to a full *year*, which makes a lot more sense. With that figure, the odds of getting struck at some point in your life are about 1 in 13,000.
So how about getting struck twice? If the odds of getting struck were independent, then using the binomial distribution you can work out that the probability of getting struck two times or more in your life would be about 1 in 360 million. The real figure seems to be lower. You had it as 1 in 7 million. I’ve also seen e.g. 1 in 9 million, but in any case we’re talking about a factor 30 lower than you’d expect from the above calculation.
So what gives? Well, this indicates that the odds *aren’t* independent. In particular, to explain this outcome, some people have to be more likely to be hit by lightning than others, probably because of where they live or because of how they spend their days. There are certain risk factors for being struck that some people avoid, while others run afoul of them a lot. Like, being outdoors in wide open spaces. This means that people who have been struck by lightning once (and survived) are more likely to be struck a second time, compared to the average person, since being struck by lightning once indicates that you likely tick a box that gives you an enhanced risk.
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