”After adjusting for potential confounders and pooling results across cohorts, higher caffeinated coffee intake was significantly associated with lower dementia risk (141 vs 330 cases per 100 000 person-years comparing the fourth [highest] quartile of consumption with the first [lowest] quartile; hazard ratio, 0.82 [95% CI, 0.76 to 0.89]) and lower prevalence of subjective cognitive decline (7.8% vs 9.5%, respectively; prevalence ratio, 0.85 [95% CI, 0.78 to 0.93]).”

So about 18% relative reduction. But if your risks are already low (e.g. active and healthy diet) the relative reduction is less impactful (e.g. 4% to 3.28%).

weird-eye-issue 8 hours ago | parent [-]

> the relative reduction is less impactful (e.g. 4% to 3.28%

That's also an 18% reduction

	▲	Xunjin 7 hours ago \| parent \| next [-]
		I think what he means is a reduction of 18% based on 4% is way less than 18% based on 80%.
	▲	infinitewars 7 hours ago \| parent \| prev \| next [-]
		Percents of percents always felt kludgey. Log probabilities (like decibans) unify this to say there is a -0.86 dB risk reduction for everybody. https://rationalnumbers.james-kay.com/?p=306 It makes the math of combining risks easier and works the same even if we're operating near 99.999% or 0.0001%
	▲	jader201 5 hours ago \| parent \| prev [-]
		That’s exactly my point. If someone is high risk, say 20%, then an 18% drop from that is 14.4%. That may justify picking up caffeine. But if you’re otherwise healthy, picking up caffeine has diminishing returns, and the downsides may not be worth it.