I saw that paragraph and clearly it's intended as some sort of advertence to the correlation/causation thing, but the thing is - if they're coming out and saying that there's merely an association here, so what? No shit? That's like somebody coming out with a study that says that there's a correlation between being alive and dying - of course there is, but it isn't an interesting question nor is it an interesting scientific relationship (in my opinion at least).

I can remember taking a neuroscience unit in my first year of uni and spending a few weeks on how important sleep is for both acute cognitive function, and longer term maintenance that is needed to deal with all the metabolites and waste products that result from such an energetic organ like the brain. This was more than 5 years ago, and yet even then it had been demonstrated that if you take mice and subject them to sleep deprivation, they will develop neurodegenerative diseases at much higher rates, and much earlier, than controls. So what exactly is this study doing? Taking longitudinal data that shows a relationship between poor sleep and neurodegenerative diseases. 2015 called and it wants its conclusions back.

Basically I'd want to see an actual experimental study where they aren't asking participants qualitative questions about their sleep quality, quantity, etc, as if individuals in the early throes of Alzheimer's could even be expected to give accurate answers. I mean honestly: Imagine asking a person with dementia to rate the previous night's sleep amount and quality on a scale of 1-10. It's laughable.

Most longitudinal studies are lazy, and to me this paper is just publishing something to publish it (welcome to modern academic life) - I cannot see how this furthers our understanding of anything.