You may be wondering why @bristoliver rather cryptically RT’d a chart that I posted last night. The answer is not just that he loves quadratic fits on log axes, but that this chart may –and I stress may– hint at a vaccine effect amongst the over 80s THREAD

WARNING: this is a long thread, and it’s a bit of a roller-coaster. We find some apparently strong patterns in the data, and then start to unpick them a bit. So if you start getting excited half way through you might find you’re less excited at the end. But we’ll see…

First we first have to go back a bit. @bristoliver posted a thread a few days ago explaining why, with a constant vaccination rate, a log plot of cases should show a quadratic form. In other words, it should fit an equation like: a + b.x + c.x^2

I meant to link in the model thread there - here it is

the quadratic coefficient – the ‘c’ in that equation – gives an estimate of the % of the population who are being newly protected by the vaccine each day. Please note ‘protected by the vaccine’, not ‘vaccinated’ – as we don't expect 100% protection after the first dose

I've had a lot of positive comments on this theory, and some helpful challenges. The most common of which was: surely a single-day effect wouldn't be big enough to cause the 'twist' in the data that we're seeing in those age groups? So I set out to find out if it was (thread)

This is one of those university / job interview 'order of magnitude' estimation problems. So feel free to disagree with any or all steps on my logic chain, and please explain why - it will help improve / refine (or falsify) the analysis.

So let's focus on the primary-school-age kids as that's where the effect is strongest. We have 3.5m 5-9 year-olds in England. I don't know how many were in school on 4th Jan - we know some regions (London / Kent etc.) didn't go back, and a lot of schools had INSET days etc

So I'm going to make a wild guess and say 40% were in school on that day. Better ideas (particularly if backed by data) very welcome. So that's about 1.4m children in school

Now ONS tells us that about 1.5% of that age group would test positive for coronavirus in early January. So that's about 20,000 kids with the virus heading into school.