Dumb and dumber

All these people exhorting amateurs to "stay in their lane" and not muddy the waters by providing analyses and articles about the COVID-19 pandemic would have an easier job of it if it wasn't for the supposed experts churning out dross on an industrial scale.

Two new forecasts for the UK caught my eye yesterday. First from IHME, it predicts a rising death toll to a daily value of over 200 by the end of the week, peaking at about 3000 later in the month (with much uncertainty). It seems to be some sort of curve-fitting exercise. They are regarded as "world-leading disease data experts" by the Guardian at least. Here is their forecast for the UK as reported in the Guardian:

and again from their own report with uncertainties (lines are at 1k intervals). So you can see they expect a strong rise and guarantee that it will go over 1k deaths later in the month.

The article describing their method is here, it's some sort of fancy curve fitting that doesn't seem to make much use of what is known about disease dynamics. I may be misrepresenting them somewhat but we'll see below what a simple disease model predicts.

Next, the famous IC group. And these are the real ones with Ferguson as last author, not the jokers who generated the silly 5700 number that got a brief bit of attention. This is the MRC-funded, WHO-collaborating lot. And what have they done here? They've also basically fitted a curve through historical death data,  and extrapolated it into the future. Their prediction is for a whopping 14k deaths with a range of 8-16k - just in the next week! A minimum of 1500 on the 7th day in that forecast too.

So why do I think these are bonkers? Because we KNOW that a lot changed two weeks ago. And we KNOW that this feeds though into deaths in about 3 weeks. Typical time from infection to death may be a little over 3 weeks but a bunch of people die significantly quicker and this means the effect of the social distancing controls should be feeding though into death rate, oh, about now.

This below is what I get from fitting my simple SEIR model to the available death data, backdated to Sunday to form a fair comparison with the IC group. 

Now, before looking at it too carefully, I do need to give a "health warning" on its validity. In particular, I don't expect the uncertainty range to be very well calibrated. I'm really focussed mainly on the best fit, and the parametric uncertainty included here is a rather subjective component. I suspect the uncertainty intervals to be rather too broad, especially at the top end (which essentially allows for continued strong growth of the epidemic, contrary to what has been seen in other countries that clamped down sooner). The corollary being that I'm pretty confident of reality lying inside the bounds, and optimistic of my median being a much better estimate of the truth than the central forecasts provided by the experts above :-)

The forecast is necessarily vague at this point, because although I believe R changed at the breakpoint, I don't yet know what it changed to. "About 1" is a plausible estimate, it might be higher but we can certainly hope that it's lower as it proved to be in Wuhan and also Italy after they clamped down.

My model predicts a total of 8k deaths next week, with a 5-95% range of 4-19k. Yes it's a wide uncertainty range, I think my prior on Rt is probably still too broad as I don't really expect to see a value lower than 0.5 or higher than 1.5 (and these are just the 1sd spread limits in the above). But I am very optimistic that the median estimate generated by this method is better than the experts have provided, and they don't seem to believe that anything in the lower half of my range is possible at all. Ominously for them, the recent data are already consistently lower than the median, albeit marginally.

I'll come back to these in a week to see how we fared.