[crazygringo]

Do you have any basis for claiming it's an outlier?

Caffeine consumption is widespread. Difficulty sleeping is widespread.

That's not saying there's a clear cause and effect -- caffeine has lots of effects, and difficulty sleeping has lots of causes.

But it's just as silly to say that any association is an outlier. And given what we know about the variability of the half-life of caffeine in the body, it's an extremely plausible possibility for a significant proportion of the population.

Not "such an outlier" at all. I'm struggling to see how you could be so immediately dismissive of it.