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Comment by gdudeman | Hacker News Reader

If you haven't seen the chart from the UK study, I highly recommend checking it out: https://erictopol.substack.com/p/the-shingles-vaccine-and-re...

When the vaccine came out in the UK, they included a hard age cutoff: Above a certain age, you weren't eligible. Below that age, you were eligible.

They looked at the probability of a dementia diagnosis over the 7 years after the vaccine was introduced.

People who were born in the "can get the vaccine" group have markedly lower rates of dementia. People in the "too old" group have higher rates. It's cut and dry. The researchers didn't separate out the people who actually got the vaccine.

It's one of those studies where you don't even need to look at the p-value to see the difference between the cohorts.

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It's not even dementia, it's shingles itself. Two friends of mine had shingles in the last year or two, one of whom has a pain threshold at a level where I'm not entirely sure he's human ("I pulled the flesh back and you could see the bare bone, it was interesting, I've never seen my insides like that before"). After hearing their description of the pain levels involved I got a shot the next week.

My older neighbour also had it a few years ago, but in her case wasn't aware it was shingles, just some rash on her face. Doctors said if they hadn't stopped it within the next few days she'd have lost her sight.

Get the shot. You probably won't need it, but if you do then you'll really need it.

So much of neurodegeneration has turned out to be the effects of latent viruses in the body. HSV-1 is correlated with developing dementia along with many respiratory viruses.

I can’t wait to see what happens when we have an Epstein-Barr virus vaccine.

Looks like there's no difference in men, but a huge difference in women? What a weird situation.

Why on earth wouldn't you need to look at the P value? You give good arguments for the soundness is the methodology, but you still need to look at the results and their statistical significance.

Their P value is 0.02, which is good but certainly not definitive. Also the effect is kind of small, 3.5% reduction in diagnoses.

I think I'm failing to understand your subtext. Obviously older people have higher rates of dementia. A study reporting that doesn't tell us anything about the effect of the vaccine.

Sorry - the older group has higher rates of dementia than the younger group when they reach the same age - so when they reach 75, they're more likely to have dementia.

I see what you mean, there's a clear gap in the fitted (regression) lines, suggesting the trend of dementia with age is different in the two groups.

But I wonder if that's just a statistical artifact. The overall trend looks the same in both groups if you ignore a couple points (ages) on either side of introducing the vaccine.

A single line appears to fit all the points well, except two points on either side of the divide.

The normalization of the age variable still looks problematic, as it requires that there is a linear dependency between age and incidence.

Both the scatter plot and also the probability graph seem to be curving upwards w.r.t age, i.e. the incidence of dementia cases seems to accelerate with age. Which at least makes a lot of intuitive sense, and would forbid just plotting in a regression line.

Having a more or less circumstantial point to arbitrarily cut your regression line in half also just begs for introducing Simpson's Paradox.

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